summaryrefslogtreecommitdiff
path: root/Master/texmf-dist/doc/latex/quantikz/quantikz.tex
blob: 1153b735af5efab855e32bdae862f2334532acd5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
\documentclass[aps,pra,10pt,nofootinbib]{revtex4}
%\pdfoutput=1
% Package(s) to include
%\listfiles
\usepackage{amsfonts,amssymb,amsmath}            % for math symbols.
\usepackage{lmodern,adjustbox}
\usepackage[skins,breakable]{tcolorbox}
\usepackage{tikz}
\usetikzlibrary{quantikz}
\tcbuselibrary{listings}
\tcbuselibrary{breakable}
\lstset{
basicstyle=\small\ttfamily,
columns=flexible,
breaklines=true
}
\usepackage[pdftex,hyperfigures,pdfpagelabels]{hyperref} 
%\lstloadlanguages{Latex}

\newtcolorbox{Code}{enhanced,fonttitle=\sffamily\bfseries\large,valign=center
,drop fuzzy shadow,sidebyside,lefthand ratio=0.4,lower separated=false}

\begin{document}

\title{Tutorial on the Quantikz Package}
\date{\today}
\author{Alastair \surname{Kay}}
\affiliation{Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK}
\email{alastair.kay@rhul.ac.uk}
\begin{abstract}
\end{abstract}
\maketitle
I've always used \href{https://arxiv.org/abs/quant-ph/0406003}{QCircuit} for typesetting quantum circuit diagrams within \LaTeX, but found the Xy-pic based notation rather impenetrable and I struggled to adapt it for my needs (this is probably my failing rather than the package's). Thus, I wanted a tikz package that could do the same. That package is Quantikz. Those familiar with QCircuit will recognise much of the notation, although it has evolved a bit (hopefully simplified!).

\section{Usage}

The quantikz package is available on CTAN, and will therefore be available through most (current) TeX distributions. Once installed, simply write
\begin{verbatim}
\usepackage{tikz}
\usetikzlibrary{quantikz}
\end{verbatim}
in the preamble of your document
Now, each time that you want to include a quantum circuit, you just enclose it in a \verb!tikzcd! or \verb!quantikz! environment. (Theoretically, there is an advantange of \verb!quantikz! over \verb!tikzcd!, but \verb!tikzcd! is retained for backwards compatibility\footnote{\texttt{quantikz} should support the external package in tikz. I've never tried it.}.)

The current version of TeX on the arXiv is not up to date enough to provide the quantikz package. When uploading your source to the arXiv, you need to obtain the file tikzlibraryquantikz.code.tex (you will always be able to locate it on your computer in the main tex directory if you have installed the package, but it should also accompany the source code of this file, and the most recent version will is available \href{http://dx.doi.org/10.17637/rh.7000520}{here}). Just include the file in the main directory of your source code.
\section{A Single Wire}
%\expandafter\def\expandafter\mname\expandafter{\getrandomletter}
Quantum circuits are laid out with a matrix notation, with cells separated by \& (just like all matrices, tables etc.\ in \LaTeX). Here, we typeset a single quantum wire.
\begin{Code}
\begin{center}
\begin{quantikz}
\lstick{$\ket{0}$} & \phase{\alpha} & \gate{H} & \phase{\beta} & \gate{H} & \phase{\gamma} & \rstick{Arbitrary\\pure state}\qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
   \begin{quantikz}
   \lstick{\ket{0}} & \phase{\alpha} & \gate{H} 
	   & \phase{\beta} & \gate{H} & \phase{\gamma}
	   & \rstick{Arbitrary\\pure state}\qw
   \end{quantikz}
\end{lstlisting}
\end{Code}
Single-qubit gates take the form \verb!\gate{H}!, with any sequence of maths allowed in the argument\footnote{See Sec.\ \ref{sec:trouble} in case you need to use \& characters in the maths.}, or, for phase gates, \verb!\phase{phase}!. The first gate should be in the second column rather than the first (so that the preceding quantum wire has somewhere to go). You {\em can} put it in the first column, it just won't have an incoming wire. 

Text can be added at the start of a quantum wire using \verb!\lstick{}!, and at the end using \verb!\rstick{}!. These are not maths environments, but you can of course insert maths delimiters such as \$.
Notice that a multi-line \verb!lstick! or \verb!rstick! is trivial\footnote{The only issue is that the height of the label will not be taken into account in the vertical spacing of quantum wires. You may have to adjust this manually. See Section \ref{sec:align} for an example of how to achieve this.}.

\subsection{Measurements}

There are several measurement devices to choose from, and the measurement basis can be specified as the parameter:
\begin{Code}
\begin{center}
\begin{quantikz}
& \meter{0} && \meterD{1} & & \measuretab{\text{out}}& & \measure{\text{basis}}
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \meter{0} && \meterD{1} && \measuretab{\text{out}} && \measure{\text{basis}}
\end{quantikz}
\end{lstlisting}
\end{Code}
Thus, in our previous circuit:
\begin{Code}
\begin{center}
\begin{quantikz}
\lstick{\ket{0}} & \phase{\alpha} & \gate{H} & \phase{\beta} & \gate{H} & \phase{\gamma} & \meter{$\ket{\pm}$}
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
\lstick{\ket{0}} & \phase{\alpha} & \gate{H} & \phase{\beta} & \gate{H} & \phase{\gamma} & \meter{$\ket{\pm}$}
\end{quantikz}
\end{lstlisting}
\end{Code}

\subsection{Wires and Arrows}

There are a few bells and whistles: \verb!\qw! connects a quantum wire from the current cell back to the previous one. Most gates have this built in (\verb!\rstick! is the notable exception). Equally, sometimes you want a `do nothing' operation, and \verb!\qw! is perfect for that. Also, you can just insert text into a cell without boxing it (as you would for a gate). This can be useful for errors, and is achieved with \verb!\push{}!. 
\begin{Code}
\begin{center}
\begin{quantikz}
\lstick{$\ket{0}$\\initial state} & \qw & \push{X} & \qw & \rstick{$\ket{1}$} \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
\lstick{$\ket{0}$\\initial state} & \qw & \push{X} & \qw & \rstick{$\ket{1}$} \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
Since we have built quantikz on top of tikzcd, any of the standard arrow commands will work. For example, after a measurement, you might want to use an arrow to report a particular measurement outcome using \verb!\arrow[r]!. The \verb!r! conveys that the arrow should head one cell to the right. You can use combinations of up (u), down (d), left (l) and right as you wish. For more styling options, see the \href{http://mirrors.ctan.org/graphics/pgf/contrib/tikz-cd/tikz-cd-doc.pdf}{tikzcd manual}.
\begin{Code}
\begin{center}
\begin{quantikz}
\lstick{$\ket{0}$\\initial state} & \qw & \push{X} & \qw & \meter{0/1} \arrow[r] & \rstick{$\ket{1}$}
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
\lstick{$\ket{0}$\\initial state} & \qw & \push{X} & \qw & \meter{0/1} \arrow[r] & \rstick{$\ket{1}$}
\end{quantikz}
\end{lstlisting}
\end{Code}

Sometimes, you may want to group a whole bunch of wires together. Use \verb!\qwbundle! instead of \verb!\qw!.
\begin{Code}
\begin{center}
\begin{quantikz}
\lstick{$\ket{0}^{\otimes n}$} &[2mm] \gate{H}\qwbundle{3} &  \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
\lstick{$\ket{0}^{\otimes n}$} &[2mm] \gate{H}\qwbundle{3} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
\noindent The size of the strike can be altered by issuing the commands \verb!\pgfkeyssetvalue{/quantikz/Strike Height}{new height}! and \verb!\pgfkeyssetvalue{/quantikz/Strike Width}{new width}!. I felt this example benefited from some additional spacing (of 2mm) on one column. For more spacing options, see Sec.\ \ref{sec:spacing}.

You can access an alternative form for the multi-qubit wire using the \verb!alternate! key:
\begin{Code}
\begin{center}
\begin{quantikz}
\lstick{$\ket{0}^{\otimes n}$} & \gate{H} \qwbundle[alternate]{}&  \qwbundle[alternate]{} 
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
\lstick{$\ket{0}^{\otimes n}$} & \gate{H} \qwbundle[alternate]{}& \control\qwbundle[alternate]{} 
\end{quantikz}
\end{lstlisting}
\end{Code}
\noindent The alternate version does not represent how many wires are supposed to be in the bundle.


\section{Multiple Qubits}

New rows are started with \textbackslash\textbackslash. If the wires don't interact, then you proceed exactly as before. Naturally, there are several gates that induce interaction between wires: \verb!\ctrl{3}! makes a control-qubit (for controlled-not, controlled-phase, controlled-$U$, etc), where the target is 3 wires below. \verb!\octrl! is near-identical, except the control circle is open, as usually used to convey being controlled off $\ket{0}$ instead of $\ket{1}$. These will need to be matched with target commands. These could be normal gates or \verb!\targ{}! (controlled-not), \verb!\control{}! (controlled-phase), \verb!\ocontrol{}! (controlled-phase, controlled off $\ket{0}$). There is also a swap gate, \verb!\swap{2}!, with target \verb!\targX{}!\footnote{For a variant, see Sec.\ \ref{sec:boxing}.}. These can be combined to give multi-controlled gates.
\begin{Code}
\begin{center}
\begin{quantikz}
\lstick{$\ket{0}$} & \gate{H} & \ctrl{1} & \gate{U} & \ctrl{1} & \swap{2} & \ctrl{1} & \qw  \\
\lstick{$\ket{0}$} & \gate{H} & \targ{} & \octrl{-1} & \control{} & \qw & \octrl{1} & \qw \\
&&&&&\targX{} & \gate{U} & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
\lstick{$\ket{0}$} & \gate{H} & \ctrl{1} & \gate{U} & \ctrl{1} & \swap{2} & \ctrl{1} & \qw  \\
\lstick{$\ket{0}$} & \gate{H} & \targ{} & \octrl{-1} & \control{} & \qw & \octrl{1} & \qw \\
&&&&&\targX{} & \gate{U} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}

If you want a gate that is one control and several targets, you may need the command \verb!\vqw{1}! (vertical quantum wire) to create vertical connections, or possibly \verb!\vcw{1}! to create the classical version.

\begin{Code}
\begin{center}
\begin{quantikz}
& \targ{} & \gate{U} & \qw \\
& \ctrl{1} \vqw{-1} & \meter{} \vcw{-1} \\
& \targ{} & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \targ{} & \gate{U} & \qw \\
& \ctrl{1} \vqw{-1} & \meter{} \vcw{-1} \\
& \targ{} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
If you want to use classical controls with both horizontal and vertical components, you can do the following.
\begin{Code}
\begin{center}
\begin{quantikz}
& \ctrl{1} & \qw & \gate{U} & \gate{V} \\
& \targ{} \vqw{1} & \meter{} & \cwbend{-1}  \\
& \targ{} & \meter{} & \cw & \cwbend{-2} &
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \ctrl{1} & \qw & \gate{U} & \gate{V} \\
& \targ{} \vqw{1} & \meter{} & \cwbend{-1} \\
& \targ{} & \meter{} & \cw & \cwbend{-2} &
\end{quantikz}
\end{lstlisting}
\end{Code}

\section{Operating on Many Qubits}

We have already met the \verb!\lstick!, \verb!\rstick!, and \verb!\gate! commands. By default, these all act on a single quantum wire. However, they also take the optional parameter \verb!wires=n! to specify that they should extend over $n$ wires. The syntax is otherwise unchanged\footnote{Strictly, the \texttt{wires=} statement should not be necessary, as this is presumed to be the default key, but it is useful for readability.}.

\begin{Code}
\begin{center}
\begin{quantikz}
\lstick[wires=3]{$\ket{0}^{\otimes 3}$} & \ctrl{1} & \meter{} \\
 & \gate[wires=2]{U} & \qw\rstick[wires=2]{$\ket{11}$} \\
 &  & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
\lstick[wires=3]{$\ket{0}^{\otimes 3}$} & \ctrl{1} & \meter{} \\
 & \gate[wires=2]{U} & \qw\rstick[wires=2]{$\ket{11}$} \\
 &  & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}

If you want to add extra width on the \verb!\gate!, use the second optional parameter to specify a width (note that this is a minimum width -- if your supplied text is wider, the box will adjust its width accordingly.
\begin{Code}
\begin{center}
\begin{quantikz}
& \gate{H} & \ctrl{1} & \meter{} \\
& \gate[wires=2][2cm]{U}  & \targ{} & \qw \\
&  & \qw & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate{H} & \ctrl{1} & \meter{} \\
& \gate[wires=2][2cm]{U}  & \targ{} & \qw \\
&  & \qw & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
Often, it is nice to be able to label the inputs and outputs on the box, which we do with the \verb!\gateinput! and \verb!\gateoutput! commands. These commands take 1 compulsory argument -- the label text. By default, this applies to a single wire, but you can again use the optional \verb!wires! parameter to extend it. The starting point is determined by where the command is placed. The width of the gate does not automatically adjust to the contents of these extra labels, so you will have to add it with the second optional parameter of \verb!\gate!.
\begin{Code}
\begin{center}
\begin{quantikz}
&\ctrl{1} & \qw \\
&\gate[wires=3][1.7cm]{U}
	\gateinput[wires=2]{$x$}
	\gateoutput[wires=2]{$x$}
	&\qw \\
& & \qw \\
&\gateinput{$y$}
\gateoutput{$y\oplus f(x)$}
&\qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
&\ctrl{1} & \qw \\
&\gate[wires=3][1.7cm]{U}
	\gateinput[2]{$x$}
	\gateoutput[wires=2]{$x$}&\qw \\
& \qw & \qw \\
&\qw\gateinput{$y$}\gateoutput{$y\oplus f(x)$}&\qw
\end{quantikz}
\end{lstlisting}
\end{Code}

You can use standard \LaTeX maths expressions for your labels. Usually, spacing can be automatically adjusted just fine. For example,

\begin{Code}
\begin{center}
\begin{quantikz}
& \gate{\sqrt{Z}} & \gate[2]{\sqrt{\textsc{swap}}} & \meter{} \\
& \gate{X}  & & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate{\sqrt{Z}} & \gate[2]{\sqrt{\textsc{swap}}} & \meter{} \\
& \gate{X}  & & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}

Sometimes, it might be that you want a multi-line label, and it should not be that each wire takes the height of those multiple lines. At this point, use the key \verb!disable auto height!. By default, each row will be assigned the height that a gate with label $U$ would be. This can be overridden by the third optional parameter of the gate command, if desired.

\begin{Code}
\begin{center}
\begin{quantikz}
\lstick{$c_0$} & \gate[3,disable auto height]{\begin{array}{c} \text{M} \\ \text{A} \\ \text{J} \end{array}} & \qw & \qw \\
\lstick{$c_1$} &  &  \gate[3,disable auto height]{\begin{array}{c} \text{M} \\ \text{A} \\ \text{J} \end{array}} & \qw \\
\lstick{$c_2$} &  &  & \qw \\
\lstick{$c_3$} & \qw &  & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
\lstick{$c_0$} & \gate[3,disable auto height]{\begin{array}{c} \text{M} \\ \text{A} \\ \text{J} \end{array}} & \qw & \qw \\
\lstick{$c_1$} &  &  \gate[3,disable auto height]{\begin{array}{c} \text{M} \\ \text{A} \\ \text{J} \end{array}} & \qw \\
\lstick{$c_2$} &  &  & \qw \\
\lstick{$c_3$} & \qw &  & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}

\subsection{Different Connections}

It is assumed that most of the time you want to connect your gates with quantum wires. However, it is possible to override that, and either use classical wires or no wire. These appear as option keys for the gate command, both of which are a comma-separated list of incoming wires that should be altered.

\begin{Code}
\begin{center}
\begin{quantikz}
& \gate[5,cwires={2,4},nwires={3}]{U} & \qw \\
& & \cw \\
& & \qw \\
& & \cw \\
& & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate[5,cwires={2,4},nwires={3}]{U} & \qw \\
& & \cw \\
& & \qw \\
& & \cw \\
& & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}

\section{Slicing}

It is often helpful to `slice' up a circuit for the sake of explaining it step by step. To do this, we provide the \verb!\slice{title}! command, which inserts a dashed vertical line after the column in which the command is added.
\begin{Code}
\begin{center}
\begin{quantikz}
& \gate{H}\slice{step}  & \ctrl{1} & \meter{} \\
& \qw       & \targ{} & \ctrl{1} & \gate{H} & \qw \\
& \qw & \qw & \targ{} & \qw & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate{H}\slice{step}  & \ctrl{1} & \meter{} \\
& \qw       & \targ{} & \ctrl{1} & \gate{H} & \qw \\
& \qw & \qw & \targ{} & \qw & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
You can also slice every step by using option \verb!slice all!, and the labels will be automatically numbered. This is likely to behave strangely unless you explicitly ensure that all rows have the same number of entries (i.e.\ short rows should have extra \& characters added).
\begin{Code}
\begin{center}
\begin{quantikz}[slice all]
& \gate{H} & \ctrl{1} & \meter{} && \\
& \qw       & \targ{} & \ctrl{1} & \gate{H} & \qw \\
& \qw & \qw & \targ{} & \qw & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[slice all]
& \gate{H}  & \ctrl{1} & \meter{} && \\
& \qw       & \targ{} & \ctrl{1} & \gate{H} & \qw \\
& \qw & \qw & \targ{} & \qw & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
If you need to adjust where the last slice is, use the optional parameter \verb!remove end slices!, which counts the number of columns fewer to add slices to. You can also change the title of each of the slices, by setting \verb!slice titles!. Include the macro \verb!\col! in your specification if you want to use the step number. Note, however, that the columns won't space themselves out to accommodate a very wide label. You can style the slicing lines with the \verb!slice style! key, and the labels with \verb!slice label style!. These can be used to rotate the labels and create a bit more space!
\begin{Code}
\begin{center}
\begin{quantikz}[slice all,remove end slices=1,slice titles=slice \col,slice style=blue,slice label style={inner sep=1pt,anchor=south west,rotate=40}]
& \gate{H} & \ctrl{1} & \meter{} && \\
& \qw       & \targ{} & \ctrl{1} & \gate{H} & \qw \\
& \qw & \qw & \targ{} & \qw & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[slice all,remove end slices=1,slice titles=slice \col,slice style=blue,slice label style={inner sep=1pt,anchor=south west,rotate=40}]
& \gate{H}  & \ctrl{1} & \meter{} && \\
& \qw       & \targ{} & \ctrl{1} & \gate{H} & \qw \\
& \qw & \qw & \targ{} & \qw & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
\noindent This also gives the possibility to alter spacing if it would otherwise be a bit too tight.
\begin{Code}
\begin{center}
\begin{quantikz}[slice all,slice style={shorten <=-0.1cm,shorten >=-0.1cm},slice label style={yshift=0.1cm}]
\lstick{$\ket{0}$} & \gate{H} & \phase{\varphi} & \gate{H} & \rstick{$\cos\frac{\varphi}{2}\ket{0}-i\sin\frac{\varphi}{2}\ket{1}$}\qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[slice all,slice style={shorten <=-0.1cm,shorten >=-0.1cm},slice label style={yshift=0.1cm}]
\lstick{$\ket{0}$} & \gate{H} & \phase{\varphi} & \gate{H} & \rstick{$\cos\frac{\varphi}{2}\ket{0}-i\sin\frac{\varphi}{2}\ket{1}$}\qw
\end{quantikz}
\end{lstlisting}
\end{Code}
\noindent If you get compile errors when trying to slice, check the last line of your matrix, and make sure it doesn't end in \textbackslash\textbackslash.

The \verb!vertical slice labels! key reorients the labels as below. 
\begin{Code}
\begin{center}
\begin{quantikz}[slice all,remove end slices=1,slice titles=slice \col,vertical slice labels]
& \gate{H} & \ctrl{1} & \meter{} && \\
& \qw       & \targ{} & \ctrl{1} & \gate{H} & \qw \\
& \qw & \qw & \targ{} & \qw & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[slice all,remove end slices=1,slice titles=slice \col,vertical slice labels]
& \gate{H}  & \ctrl{1} & \meter{} && \\
& \qw       & \targ{} & \ctrl{1} & \gate{H} & \qw \\
& \qw & \qw & \targ{} & \qw & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}

\section{Spacing}\label{sec:spacing}

\subsection{Local Adjustment}

There are several different ways in which we can manipulate the spacing of a diagram. Adding space to an individual row or column can be done in the standard way of tables in LaTeX. Here we add 2cm of space to the column between the $H$ and $X$ gates, and 1cm of space between the top two rows.
\begin{Code}
\begin{center}
\begin{quantikz}
& \gate{H} &[2cm] \gate{X} & \gate{H} & \qw \\[1cm]
& \gate{X} & \gate{Z} & \gate{Z} &\qw \\
& \gate{X} & \gate{Z} & \gate{Z} & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate{H} &[2cm] \gate{X} & \gate{H} & \qw \\[1cm]
& \gate{X} & \gate{Z} & \gate{Z} & \qw \\
& \gate{X} & \gate{Z} & \gate{Z} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
If you don't know how much space you need, but it should be determined by the size of some text, you can use \verb!\hphantom{}! (widens the gate, in a similar way to \verb!\gate[1cm]{}!) or \verb!\hphantomgate{}! (increases the length of a wire) for horizontal spacing, and \verb!\ghost{}! for vertical spacing.
\begin{Code}
\begin{center}
\begin{quantikz}
& \gate{X} \hphantom{very wide} & \gate{X} & \hphantomgate{wide}\qw & \gate{X}
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
 & \gate{X} \hphantom{very wide} & \gate{X} & \hphantomgate{wide}\qw & \gate{X}
\end{quantikz}
\end{lstlisting}
\end{Code} 

\subsection{Global Adjustment}

Standard tikz commands facilitate a global adjustment of row and column spacing. For example, a ridiculous horizontal spacing:
\begin{Code}
\begin{center}
\begin{quantikz}[column sep=1cm]
& \gate{H} & \phase{\beta} & \gate{H} & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[column sep=1cm]
& \gate{H} & \phase{\beta} & \gate{H} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
This specifically adjusts the \emph{gap} between the rows and columns, not the distance between the centres of the rows and columns. Depending on what gates you have on each wire, the spacing may not be the same between each wire. Sometimes this is desirable, particularly if a gate in one particular row is much larger than anything in the other rows. At other times, it just makes your diagram look a little odd. For example, look at the gap between the top two wires and the bottom two wires:
\begin{Code}
\begin{center}
\begin{quantikz}[row sep=0.1cm]
& \gate{X} & \ctrl{1} & \gate{X} & \qw \\
& \qw & \control{} & \qw & \qw \\
& \gate{X} & \qw & \qw & \qw \\
& \gate{H} & \qw & \qw & \qw 

\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[row sep=0.1cm]
& \gate{X} & \ctrl{1} & \gate{X} & \qw \\
& \qw & \control{} & \qw & \qw \\
& \gate{X} & \qw & \qw & \qw \\
& \gate{H} & \qw & \qw & \qw 
\end{quantikz}
\end{lstlisting}
\end{Code}
If you want to make sure that every quantum wire is equally spaced, do the following to \verb!row sep!:
\begin{Code}
\begin{center}
\begin{quantikz}[row sep={0.6cm,between origins}]
& \gate{X} & \ctrl{1} & \gate{X} & \qw \\
& \qw & \control{} & \qw & \qw \\
& \gate{X} & \qw & \qw & \qw \\
& \gate{H} & \qw & \qw & \qw 

\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[row sep={0.6cm,between origins}]
& \gate{X} & \ctrl{1} & \gate{X} & \qw \\
& \qw & \control{} & \qw & \qw \\
& \gate{X} & \qw & \qw & \qw \\
& \gate{H} & \qw & \qw & \qw 
\end{quantikz}
\end{lstlisting}
\end{Code}
This is particularly useful to achieve alignment of several circuits, as in \ref{sec:align}.

\subsection{Alignment}\label{sec:align}

How do we centre a circuit diagram? Simply surround it with \verb!\begin{center}! and \verb!\end{center}! commands, or within any standard equation environment.

Vertical alignment between different circuits can be more fiddly, depending on how much of a perfectionist you are. Sometimes, they work immediately, but the wires don't always align perfectly with each other. Generally the problem is that the highest gate in each row is different (here, the LHS is missing an $X$ gate on the second row)
\begin{Code}
\begin{center}
\begin{quantikz}
& \gate{X} & \ctrl{1} & \qw \\
& \qw & \targ{} & \qw
\end{quantikz}
\begin{quantikz}=\end{quantikz}\begin{quantikz}
& \ctrl{1} & \gate{X} & \qw \\
& \targ{}  & \gate{X} & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate{X} & \ctrl{1} & \qw \\
& \qw & \targ{} & \qw
\end{quantikz}
=\begin{quantikz}
& \ctrl{1} & \gate{X} & \qw \\
& \targ{}  & \gate{X} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
\noindent  Ensuring an even spacing between rows, as described in Sec.\ \ref{sec:spacing}, can help (but is not always appropriate). Often the easiest is to fudge it using the \verb!\ghost! command which will add a 0-width gate of the height corresponding to its argument. So, having identified the problem with the above circuit, we can replace it with:
\begin{Code}
$$
\begin{quantikz}
& \gate{X} & \ctrl{1} & \qw \\
& \ghost{X}\qw & \targ{} & \qw
\end{quantikz}
=\begin{quantikz}
& \ctrl{1} & \gate{X} & \qw \\
& \targ{}  & \gate{X} & \qw
\end{quantikz}
$$
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate{X} & \ctrl{1} & \qw \\
& \ghost{X}\qw & \targ{} & \qw
\end{quantikz}
=\begin{quantikz}
& \ctrl{1} & \gate{X} & \qw \\
& \targ{}  & \gate{X} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}

If you cannot identify the offending gate, and particularly if the operation is not a standard \verb!\gate! command, you might be better off combining the two circuits in a single circuit with no wires joining the two parts. The spacing works better if your circuit has an odd number of wires, otherwise you have to add an extra row in the middle, and then change the spacing of that row with its neighbours.
\begin{Code}
\begin{center}
\begin{quantikz}
& \qw & \ctrl{2} & \qw&&& \ctrl{2} & \gate{Z} & \qw \\[-0.3cm]
&&&&=&\\[-0.3cm]
& \gate{Z} & \targ{} & \qw&&& \targ{}  & \gate{Z} & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \qw & \ctrl{2} & \qw&&& \ctrl{2} & \gate{Z} & \qw \\[-0.3cm]
&&&&=&\\[-0.3cm]
& \gate{Z} & \targ{} & \qw&&& \targ{}  & \gate{Z} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}

\subsubsection{Perfecting Vertical Alignment}

If you want total control over vertical alignment between several different circuits, the trick is to use the \verb!baseline! key. All the baselines of different items are placed on the same level. This is particularly helpful if you give certain wires in the circuit a name, and that will let you place the baseline directly on a level with that wire.

To name a wire as `name', place an \verb!\alias{name}! command in any cell which is either empty, or contains a \verb!\qw!, \verb!\cw! or \verb!\push! \emph{only}, and place it before that command\footnote{Alternatively, for any node that accepts tikz styling parameters directly as an option, passing the option \texttt{alias=name} should do.}. That lets you align circuit identities such as
\begin{Code}
$$
\begin{quantikz}[baseline=(W.base)]
\lstick{\ket{0}} & \qw & \ctrl{1} & \qw \\
& \gate{H} & \targ{} & \alias{W} \qw
\end{quantikz}
\equiv
\begin{quantikz}[baseline=(W.base)]
& \gate{H} & \gate{X} & \alias{W} \qw
\end{quantikz}
$$
\tcblower
\begin{lstlisting}
$$
\begin{quantikz}[baseline=(W.base)]
\lstick{\ket{0}} & \qw & \ctrl{1} & \qw \\
& \gate{H} & \targ{} & \alias{W} \qw
\end{quantikz}
\equiv\begin{quantikz}[baseline=(W.base)]
& \gate{H} & \gate{X} & \alias{W} \qw
\end{quantikz}
$$
\end{lstlisting}
\end{Code}
This has aligned the bottom wire of the first circuit with the wire in the second circuit, making the correspondence more obvious. However, the $\equiv$ sign is now in the wrong place, with its baseline placed at the same point as the baseline of the circuits. We can fix this with a vertical shift of the two diagrams. We demonstrate two different ways of achieving the same effect (the only important feature is that both diagrams have the same shift).
\begin{Code}
$$
\begin{quantikz}[baseline={($(W.base)+0.3*(0,1cm)$)}]
\lstick{\ket{0}} & \qw & \ctrl{1} & \qw \\
& \gate{H} & \targ{} & \alias{W} \qw
\end{quantikz}
\equiv\begin{quantikz}[baseline={([yshift=0.3cm]new.base)}]
& \gate{H} & \gate{X} & \alias{new} \qw
\end{quantikz}
$$
\tcblower
\begin{lstlisting}
$$
\begin{quantikz}[baseline={($(W.base)+0.3*(0,1cm)$)}]
\lstick{\ket{0}} & \qw & \ctrl{1} & \qw \\
& \gate{H} & \targ{} & \alias{W} \qw
\end{quantikz}
\equiv\begin{quantikz}[baseline={([yshift=0.3cm]new.base)}]
& \gate{H} & \gate{X} & \alias{new} \qw
\end{quantikz}
$$
\end{lstlisting}
\end{Code}

If you have an even number if wires, you might choose to calculate the centre of the circuit from \verb!current bounding box.center!, or you could perform a calculation to average the position of two wires. This calculation can then be adjusted to take into account the desire to vertically align on the centre of an equals sign rather than the baseline (which is below the bottom of the equals)

\begin{Code}
$$
\begin{quantikz}[baseline={($(W.base)!.5!(W2.base) - height("$\vcenter{}$")*(0,1pt)$)}]
& \gate{X} & \ctrl{1} & \alias{W} \qw \\
& \ghost{X}\qw & \targ{} & \alias{W2} \qw
\end{quantikz}
=\begin{quantikz}[baseline={($(W.base)!.5!(W2.base) - height("$\vcenter{}$")*(0,1pt)$)}]
& \ctrl{1} & \gate{X} & \qw \\
& \targ{}  & \gate{X} & \qw
\end{quantikz}
$$
\tcblower
\begin{lstlisting}
$$
\begin{quantikz}[baseline={($(W.base)!.5!(W2.base) - height("$\vcenter{}$")*(0,1pt)$)}]
& \gate{X} & \ctrl{1} & \alias{W} \qw \\
& \ghost{X}\qw & \targ{} & \alias{W2} \qw
\end{quantikz}
=\begin{quantikz}[baseline={($(W.base)!.5!(W2.base) - height("$\vcenter{}$")*(0,1pt)$)}]
& \ctrl{1} & \gate{X} & \qw \\
& \targ{}  & \gate{X} & \qw
\end{quantikz}
$$
\end{lstlisting}
\end{Code}

For more details on the possible syntax here, see the \verb!calc! library in tikz.

\subsection{Scaling}

When we altered the spacing, that left all the gate elements, text etc.\ the same size, and just altered the spacing between them. If you want to override the standard size of a circuit (gate elements, text and spacing), you can make it a node inside a \verb!tikzpicture!:
\begin{Code}
\begin{center}
\begin{tikzpicture}
\node[scale=1.5] {
\begin{quantikz}
& \gate{H} & \phase{\beta} & \gate{H} & \qw
\end{quantikz}
};
\end{tikzpicture}
\end{center}
\tcblower
\begin{lstlisting}
\begin{tikzpicture}
\node[scale=1.5] {
\begin{quantikz}
& \gate{H} & \phase{\beta} & \gate{H} & \qw
\end{quantikz}
};
\end{tikzpicture}
\end{lstlisting}
\end{Code}
It's also possible to rescale to a fixed width, so long as you declare the \verb!adjustbox! package in the document preamble.
\begin{Code}
\begin{center}
\begin{adjustbox}{width=0.8\textwidth}
\begin{quantikz}
& \gate{H} & \phase{\beta} & \gate{H} & \qw
\end{quantikz}
\end{adjustbox}
\end{center}
\tcblower
\begin{lstlisting}
\begin{adjustbox}{width=0.8\textwidth}
\begin{quantikz}
& \gate{H} & \phase{\beta} & \gate{H} & \qw
\end{quantikz}
\end{adjustbox}
\end{lstlisting}
\end{Code}


\section{Typesetting}

\subsection{Global Styling}

Global properties that affect all circuit elements of a given type can be affected through \verb!tikzset!.
\begin{Code}
\begin{center}
\tikzset{
	operator/.append style={fill=red!20},
	my label/.append style={above right,xshift=0.3cm},
	phase label/.append style={label position=above}
}
\begin{quantikz}
& \gate{H} & \phase{\beta} & \gate{H} & \qw & \meter{$\ket{\pm}$}
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\tikzset{
  operator/.append style={fill=red!20},
  my label/.append style={above right,xshift=0.3cm},
  phase label/.append style={label position=above}
}
\begin{quantikz}
& \gate{H} & \phase{\beta} & \gate{H} & \qw & \meter{$\ket{\pm}$}
\end{quantikz}
\end{lstlisting}
\end{Code}
The global styles are:
\begin{center}
\begin{tabular}{c|c}
Style Name & Affected Command(s)	\\
\hline
operator & \verb!\gate!	\\
meter & \verb!\meter! \\
slice & \verb!\slice! \\
wave & \verb!\wave! \\
leftinternal	& \verb!\gateinput! \\
rightinternal	& \verb!\gateoutput! \\
dm & left braces (\verb!\gateoutput!,\verb!\lstick!) \\
dd & right braces (\verb!\gateinput!,\verb!\rstick!) \\
phase & \verb!\phase!, \verb!\control! \\
ophase & \verb!\ophase!, \verb!\ocontrol! \\
circlewc & \verb!\targ! \\
crossx2 & \verb!\swap!,\verb!\targX! \\
my label & measurement bases in \verb!\meter! \\
phase label & phases in \verb!\phase! \\
gg label & main gate label in \verb!\gate! \\
group label & label in \verb!\gategroup!
\end{tabular}
\end{center}

There are two keys that change styles globally: `thin lines' to make the lines thin, more in keeping with what QCircuit produced
\begin{Code}
\begin{center}
\begin{quantikz}[thin lines]
& \ctrl{1} & \qw & \ctrl{1} & \qw & \qw \\
& \targ{} & \gate{R_z(-\theta/2)} & \targ{} & \gate{R_z(\theta/2)} & \meter{}
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[thin lines]
& \ctrl{1} & \qw & \ctrl{1} & \qw & \qw \\
& \targ{} & \gate{R_z(-\theta/2)} & \targ{} 
  & \gate{R_z(\theta/2)} & \meter{}
\end{quantikz}
\end{lstlisting}
\end{Code}
\noindent and `transparent', should you want the background of all the gates to be transparent:
\begin{Code}
\begin{center}
\begin{quantikz}[transparent]
& \ctrl{1} & \qw & \ctrl{1} & \qw & \qw \\
& \targ{} & \gate{R_z(-\theta/2)} & \targ{} & \gate{R_z(\theta/2)} & \meter{}
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[transparent]
& \ctrl{1} & \qw & \ctrl{1} & \qw & \qw \\
& \targ{} & \gate{R_z(-\theta/2)} & \targ{} 
  & \gate{R_z(\theta/2)} & \meter{}
\end{quantikz}
\end{lstlisting}
\end{Code}

One place where this might be useful is as a ``pass-through'' on a gate, such as 
\begin{Code}
\begin{center}
\begin{quantikz}[transparent]
& \gate[2]{J_{12}} & \gate[3,label style={yshift=0.2cm}]{J_{13}} & \qw & \qw	\\
& & \linethrough &\gate[2]{J_{23}} & \qw \\
& \qw &&& \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[transparent]
& \gate[2]{J_{12}} & \gate[3,label style={yshift=0.2cm}]{J_{13}} & \qw & \qw	\\
& & \linethrough &\gate[2]{J_{23}} & \qw \\
& \qw &&& \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
While the \verb!\linethrough! would normally be hidden behind the gate, making the gate transparent leaves the line visible. Then one just has to move the $J_{13}$ label (see next section).

\subsection{Per-Gate Styling}

Individual gates can be modified using optional arguments of the calling function. 
\begin{Code}
\begin{center}
\begin{quantikz}
& \gate[style={fill=red!20},label style=cyan]{H} & \phase[green,label position=above]{\beta} & \gate{H} & \qw & \meter{$\ket{\pm}$}
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate[style={fill=red!20},label style=cyan]{H} 
  & \phase[green,label position=above]{\beta} 
  & \gate{H} & \qw & \meter{$\ket{\pm}$}
\end{quantikz}
\end{lstlisting}
\end{Code}
The specific syntax varies a little depending on the type of gate
\begin{center}
\begin{tabular}{p{0.4\textwidth}|p{0.4\textwidth}}
gates that don't accept formatting parameters & \verb!\qw!,\verb!\vqw!,\verb!\qwbundle!,\verb!\cw!,\verb!\vcw!,\verb!\cwbend!,\verb!\push!	\\
\hline
gates that accept tikz node formatting keys directly in optional argument & \verb!\phase!, \verb!\control!, \verb!\ocontrol!, \verb!\targ!, \verb!\targX!, \verb!\meter!, \verb!\meterD!, \verb!\measure!, \verb!\measuretab!, \verb!\wave! \\
\hline
gates that accept node formatting keys as \verb!label style! key in optional argument & \verb!\gate!, \verb!\slice!, \verb!\lstick!, \verb!\rstick!, \verb!\gategroup!, \verb!\gateinput!, \verb!\gateoutput!
\end{tabular}
\end{center}
Those that accept the \verb!label style! key also accept a second key for formatting other elements of the display
\begin{center}
\begin{tabular}{c|cc}
\verb!\gate!,\verb!\gategroup! & \verb!style! & styles the box	\\
\verb!\slice! & \verb!style! & styles the line\\
\verb!\lstick!,\verb!\rstick!,\verb!\gateinput!,\verb!\gateoutput! & \verb!braces! & styles the brace
\end{tabular}
\end{center}
If you want to input several styling parameters with one of these keys, just group them together in a set of curly braces, \{\}. Typical styling parameters include \verb!draw=! specifying line colour, \verb!fill=!, specifying fill colour, \verb!inner xsep=! and \verb!inner ysep=! specifying horizontal and vertical margins respectively, \verb!xshift=! and \verb!yshift=! for adjusting horizontal and vertical positioning. Beyond that, the \href{http://mirrors.ctan.org/graphics/pgf/base/doc/pgfmanual.pdf}{tikz manual} is your friend!

This styling is really quite flexible, as we can override the default shapes with anything that we want:
\begin{Code}
\begin{center}
\tikzset{
	group-1-5/.append style={starburst,fill=yellow,draw=red,line width=2pt,inner ysep=-15pt}
}
\begin{quantikz}[row sep=0.3cm,column sep=0.3cm]%
& \gate{H} & \ctrl{2}& \qw & \gate[3,style={starburst,fill=yellow,draw=red,line width=2pt,inner xsep=-4pt,inner ysep=-5pt},label style=cyan]{\text{noise}} & \ctrl{3} & \qw  & \qw & \qw\\
\lstick{$\ket{0}$} & \qw & \targ{} & \qw & \qw & \qw & \ctrl{3} & \qw & \qw \\
\lstick{$\ket{0}$} & \qw & \targ{}& \qw & \qw & \qw & \qw & \ctrl{2} & \qw\\
&&&&\lstick{$\ket{0}$} & \targ{} & \targ{} & \qw & \meter{} \\
&&&&\lstick{$\ket{0}$} & \qw & \targ{} & \targ{} & \meter{} 
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[row sep=0.3cm,column sep=0.3cm]%
& \gate{H} & \ctrl{2}& \qw & 
  \gate[3,style={starburst,fill=yellow,draw=red,line width=2pt,inner xsep=-4pt,inner ysep=-5pt},
    label style=cyan]{\text{noise}} & \ctrl{3} & \qw  & \qw& \qw\\
\lstick{$\ket{0}$} & \qw & \targ{} & \qw & \qw & \qw & \ctrl{3} & \qw & \qw \\
\lstick{$\ket{0}$} & \qw & \targ{}& \qw & \qw & \qw & \qw & \ctrl{2} & \qw\\
&&&&\lstick{$\ket{0}$} & \targ{} & \targ{} & \qw & \meter{} \\
&&&&\lstick{$\ket{0}$} & \qw & \targ{} & \targ{} & \meter{} 
\end{quantikz}
\end{lstlisting}
\end{Code}
% We can also supplement with standard tikz commands by using the `execute at end picture' key. The cells of the matrix contain nodes called \verb!\tikzcdmatrixname-i-j!, where i is the row number and j is the column number. Thus,
% \begin{Code}
% \begin{center}
% \begin{quantikz}[row sep=0.3cm,column sep=0.3cm,execute at end picture={
% 	\node [fit=(\tikzcdmatrixname-1-6)(\tikzcdmatrixname-4-6)(\tikzcdmatrixname-5-9),draw,dashed,inner sep=4pt,label={[yshift=0.3cm]above:syndrome extraction}] {};
% }]
% & \gate{H} & \ctrl{2}& \qw & \gate[3,style={starburst,fill=yellow,draw=red,line width=2pt,inner xsep=-4pt,inner ysep=-5pt}]{\text{noise}} & \ctrl{3} & \qw  & \qw& \qw\\
% \lstick{$\ket{0}$} & \qw & \targ{} & \qw & \qw & \qw & \ctrl{3} & \qw & \qw \\
% \lstick{$\ket{0}$} & \qw & \targ{}& \qw & \qw & \qw & \qw & \ctrl{2} & \qw\\
% &&&&\lstick{$\ket{0}$} & \targ{} & \targ{} & \qw & \meter{} \\
% &&&&\lstick{$\ket{0}$} & \qw & \targ{} & \targ{} & \meter{} 
% \end{quantikz}
% \end{center}
% \tcblower
% \begin{lstlisting}
% \begin{quantikz}[row sep=0.3cm,column sep=0.3cm,execute at end picture={
% 	\node [fit=(\tikzcdmatrixname-1-6)(\tikzcdmatrixname-4-6)(\tikzcdmatrixname-5-9),draw,dashed,inner sep=4pt,label={[yshift=0.3cm]above:syndrome extraction}] {};
% }]
% & \gate{H} & \ctrl{2}& \qw & \gate[3,style={starburst,fill=yellow,draw=red,line width=2pt,inner xsep=-4pt,inner ysep=-5pt}]{\text{noise}} & \ctrl{3} & \qw  & \qw& \qw\\
% \lstick{$\ket{0}$} & \qw & \targ{} & \qw & \qw & \qw & \ctrl{3} & \qw & \qw \\
% \lstick{$\ket{0}$} & \qw & \targ{}& \qw & \qw & \qw & \qw & \ctrl{2} & \qw\\
% &&&&\lstick{$\ket{0}$} & \targ{} & \targ{} & \qw & \meter{} \\
% &&&&\lstick{$\ket{0}$} & \qw & \targ{} & \targ{} & \meter{} 
% \end{quantikz}
% \end{lstlisting}
% \end{Code}

\subsection{Boxing/Highlighting Parts of a Circuit}\label{sec:boxing}

It is often useful to highlight parts of a circuit. We do this with the \verb!\gategroup! command. The optional parameters \verb!wires! (again, the default) and \verb!steps! specify the number of rows and columns that the group spans respectively. The mandatory argument is the label for the box (although this can be empty). The top-left corner of the box coincides with the cell in which the command is placed.
\begin{Code}
\begin{center}
\begin{quantikz}
& \gate{H} & \ctrl{1} & \gate{H}\gategroup[wires=2,steps=3,style={inner sep=6pt}]{reversed c-{\sc not}} & \ctrl{1} & \gate{H} & \ctrl{1} & \qw & \qw \\
& \qw & \targ{} & \gate{H} & \targ{} & \gate{H} & \targ{} & \gate{H} & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate{H} & \ctrl{1} & \gate{H}\gategroup[wires=2,steps=3,style={inner sep=6pt}]{reversed c-{\sc not}} & \ctrl{1} & \gate{H} & \ctrl{1} & \qw & \qw \\
& \qw & \targ{} & \gate{H} & \targ{} & \gate{H} & \targ{} & \gate{H} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
By default, this box is drawn on top of the circuit itself. If you want it to be behind (for example, should you want it to have a background colour), then use the \verb!background! option.
\begin{Code}
\begin{center}
\begin{quantikz}
& \gate{H} & \ctrl{1}\gategroup[2,steps=3,style={dashed,rounded corners,fill=blue!20, inner xsep=2pt},background]{{\sc swap}} & \targ{} & \ctrl{1} & \qw & \qw \\
& \qw & \targ{} & \ctrl{-1} & \targ{} & \gate{H} & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate{H} & \ctrl{1}\gategroup[2,steps=3,style={dashed,rounded corners,fill=blue!20, inner xsep=2pt},background]{{\sc swap}} & \targ{} & \ctrl{1} & \qw & \qw \\
& \qw & \targ{} & \ctrl{-1} & \targ{} & \gate{H} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
The \verb!label style! key can be used to tune the label's properties, including positioning. For example,
\begin{Code}
\begin{center}
\begin{quantikz}
& \gate{H} & \ctrl{1}\gategroup[2,steps=3,style={dashed,rounded corners,fill=blue!20, inner xsep=2pt},background,label style={label position=below,anchor=north,yshift=-0.2cm}]{{\sc swap}} & \targ{} & \ctrl{1} & \qw & \qw \\
& \qw & \targ{} & \ctrl{-1} & \targ{} & \gate{H} & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate{H} & \ctrl{1}\gategroup[2,steps=3,style={dashed,rounded corners,fill=blue!20, inner xsep=2pt},background,label style={label position=below,anchor=north,yshift=-0.2cm}]{{\sc swap}} & \targ{} & \ctrl{1} & \qw & \qw \\
& \qw & \targ{} & \ctrl{-1} & \targ{} & \gate{H} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
Note that it is often good to use \verb!anchor=mid! for label anchors because if you have multiple labels, this will help get them horizontally aligned. It just means you have to use some \verb!yshift! to move the label off the border around the gategroup.


At this point, we mention an extra option for the gate command. The \verb!swap! keyword turns the gate into a variant of a {\sc swap} gate which explicitly shows the wires (the \verb!wires! setting is fixed to 2, overriding any value you might supply).
\begin{Code}
\begin{center}
\begin{quantikz}
& \gate{H} & \gate[swap]{} & \qw & \qw \\
& \qw &  & \gate{H} & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate{H} & \gate[swap]{} & \qw & \qw \\
& \qw &  & \gate{H} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
%\noindent Here the \texttt{fullwidth} command is helpful for getting the symmetry of the swap gate correct in terms of how much goes above the top wire, and how much below the bottom wire.
\section{Otherwise Undocumented Features}
A wave for separating rows. Do we really need this? Perhaps not, but it's fun!
\begin{Code}
\begin{center}
\begin{quantikz}
& \gate{H} & \ctrl{3} & \ \ldots\ \qw & \qw & \gate{H} & \qw \\
\wave&&&&&&\\
& \gate{H} & \qw & \ \ldots\ \qw & \ctrl{1} & \gate{H} & \qw \\
& \qw & \gate{U} & \ \ldots\ \qw & \gate{U^k} & \qw & \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}
& \gate{H} & \ctrl{3} & \ \ldots\ \qw & \qw & \gate{H} & \qw \\
\wave&&&&&&\\
& \gate{H} & \qw & \ \ldots\ \qw & \ctrl{1} & \gate{H} & \qw \\
& \qw & \gate{U} & \ \ldots\ \qw & \gate{U^k} & \qw
\end{quantikz}
\end{lstlisting}
\end{Code}

\section{Converting from QCircuit}

I've updated all of my existing teaching materials from QCircuit to Quantikz with very little trouble. There are a few standard replacements:
\begin{center}
\begin{tabular}{c|c}
QCircuit notation & Quantikz notation \\
\hline
\verb!\QCircuit @C=n @R=m {#}! & \verb!\begin{quantikz}[row sep=m,col sep=n]#\end{quantikz}!	\\
\verb!\multigate{n}! & \verb!\gate[n+1]!	\\
\verb!\targ! & \verb!\targ{}! \\
\verb!\control! & \verb!\control{}! \\
\verb!\meter! & \verb!\meter{}! \\
\verb!\measureD! & \verb!\meterD{}! \\
\end{tabular}
\end{center}
Updating the \verb!\gategroup! command requires a little more care since the first two arguments have to be removed, and the command placed in the correct cell, at which point \verb!\gategroup{i}{j}{k}{l}{m}! becomes \verb!\gategroup[wires=k+1-i,steps=l+1-j]!. My primary use of gategroup was to achieve the effect now achieved with \verb!\lstick[k+1-i]!.

It should not be necessary to use \verb!\ghost! commands in the way they were used in QCircuit. The \verb!\cghost! and \verb!\nghost! commands have been replaced by option keys for the gate command, \verb!cwires! and \verb!nwires! respectively.

\section{Troubleshooting}\label{sec:trouble}
\begin{itemize}
\item Have you checked that all commands that need them are followed by an empty argument, \{\}? Things like \verb!meter!, \verb!\control! (basically, those that can accept an optional styling parameter) look like they don't take any parameters, but they have to be followed by the pair of braces or you'll get very odd effects.
\item If you get a whole bunch of unexpected text in one of your cells instead of a gate, make sure that the gate command is the first command in the cell, and that other commands (such as \verb!\qwbundle!) appear after.
\item If you're getting errors about cells not being found (and especially if you're doing any slicing), check that your last row doesn't end with \textbackslash\textbackslash, and make sure that your last row contains as many cells (even if they're empty) as there are columns in the circuit.
\item If you are trying to typeset your circuit inside some sort of tabular or align environment and are getting an error ``single ampersand used with wrong catcode'', trying adding the \verb![ampersand replacement=\&]! option to tikzcd, and instead of separating every cell by \&, use \textbackslash\&. This can also be useful if you want to insert a normal matrix as a gate
\begin{Code}
\begin{center}
\begin{quantikz}[ampersand replacement=\&]
\lstick{$\ket{0}$} \& \gate{\left(\begin{array}{cc} \alpha & \beta \\ \beta & -\alpha \end{array}\right)} \& \ctrl{1} \& \gate{U_1} \& \qw \\
\lstick{$\ket{0}$} \& \qw \& \targ{} \& \gate{U_2} \& \qw
\end{quantikz}
\end{center}
\tcblower
\begin{lstlisting}
\begin{quantikz}[ampersand replacement=\&]
\lstick{$\ket{0}$} \& \gate{\left(\begin{array}{cc} \alpha & \beta \\ \beta & -\alpha \end{array}\right)} \& \ctrl{1} \& \gate{U_1} \& \qw \\
\lstick{$\ket{0}$} \& \qw \& \targ{} \& \gate{U_2} \& \qw
\end{quantikz}
\end{lstlisting}
\end{Code}
Beamer is particularly annoying with doing this. It probably helps to issue a global command
\begin{lstlisting}
\tikzcdset{
	every matrix/.style={ampersand replacement=\&}
}
\end{lstlisting}
Beamer is particularly annoying with doing this. It probably helps to issue a global command
\begin{lstlisting}
\tikzcdset{
	every matrix/.style={ampersand replacement=\&}
}
\end{lstlisting}
somewhere in your document preamble. The tikzcd manual suggests another possible strategy, but I haven't had much success with it.
\item If you have a \verb!\cwbend! in the bottom right cell of the matrix, sometimes you get an error (I have no understanding of why). Add an extra \& after, and all seems to be well.
\item If you're using transparency, and the width of gates seems to be greater than you expected, it may be worthwhile removing the .aux file and recompiling. If your tex editor isn't good at resetting the .aux file, the system may be remembering older widths.
\item The code provides definitions for \verb!\bra!, \verb!\ket!, \verb!\proj!, \verb!\braket!. If you don't like them, just define your own versions \emph{before} you load the quantikz library.
\end{itemize}

For any bug reports (please make sure you've checked the above list first!) or feature requests, please contact alastair.kay@rhul.ac.uk.

\section{Citation}

If you found this package useful, please consider citing the arXiv version of this document, arXiv:1809.03842.


\end{document}