Introduction to Quantum Computing with Qiskit (with IBM Quantum)

1. 00:00hi again so now that you have done a recap of the fundamentals of quantum computing
2. 00:06you are ready to start doing the handsome part and the first
3. 00:10tool that we will use today it's the quantum composer
4. 00:23so let's go back to the platform that we have already explored before
5. 00:29let's go to the first tool so i will just click on launch composer
6. 00:36and you will probably see something different than these but
7. 00:40i have prepared it so that we can see
8. 00:43piece by piece what we can use so here in view you have
9. 00:48different things that you can set up the first one is what
10. 00:52are the things that you're going to see
11. 00:54so the first one that we're going to explore it's the graphical
12. 00:57editor and when we click on it it appears here
13. 01:02yes about the style you can also change the theme and you can
14. 01:08make it colored or not
15. 01:11depending on what you like best
16. 01:15and so here basically we have a graphical editor it's line
17. 01:19represents our quantum register and then the lines below represent
18. 01:23the classical register where we will store the output
19. 01:27of the measurements we can click on the first one and we can
20. 01:32add as many as we want so for instance now let's add
21. 01:37up to five Qubits it's the biggest
22. 01:43processor we have access to
23. 01:45i'm going to delete what we have here already we can give
24. 01:51it a name so that it's saved everything we do it's automatically
25. 01:56saved when we do some changes but you have to remember to give it a name
26. 02:01as you can see we can also
27. 02:07add more registers if we measure Qubits we will need
28. 02:11as many classical register as quantum registers so that's why
29. 02:15i have added here five so the number indicates how many classical registers we have
30. 02:21and now let's build our first circuit so here on the left you have all the
31. 02:30different gates that you can use for building your circuit
32. 02:37depending on how many Qubits you have as you see there are some that
33. 02:42appear in gray so for instance this
34. 02:48gate here needs four Qubits so automatically when you don't
35. 02:52have enough Qubits you cannot select it
36. 02:56and we have different operations so we have
37. 03:01the most widely use gates
38. 03:05combining them we can create almost any gate
39. 03:09and you also have some other operations such as initializing
40. 03:14to zero you have barriers you have measurements etcetera
41. 03:21and also there is the possibility to create
42. 03:24a custom operation
43. 03:29but we will talk about that a little bit later in the example
44. 03:33so now for the first example that we are going to do we will
45. 03:36only need two Qubits so i'm going to
46. 03:40decrease the number of classical registers and Qubits we have two Qubits q[0], q[1]
47. 03:45one and we have two classical registers
48. 03:49so the first thing that we're going to do is using Hadamard gate
49. 03:53that you already saw in the recap
50. 03:56and we're going to put it apply it to the first Qubit both
51. 04:01of them are initialized to zero automatically if you don't do anything else
52. 04:06you have to assume that by default they are initialized to zero
53. 04:10and now we are going to apply a
54. 04:13CNOT gate and we are going to measure both Qubits
55. 04:20here you can change
56. 04:24the visualizations seed let's put whatever
57. 04:31and you can set up the rest of settings of your experiment
58. 04:37so first thing we have to do it's choosing a Backend that has
59. 04:41enough Qubits for us to execute
60. 04:44this experiment and in this case we're going to be using the
61. 04:48qasm simulator as i explained earlier it's a simulator that mimics the
62. 04:54behaviour of an actual device so this is the one that we are going to use
63. 04:59because the rest of the devices
64. 05:02are available for free for everyone with an account so there
65. 05:07might be a queue usually you have a five units five jobs that
66. 05:15that you can execute simultaneously so when you send the job to a Backend
67. 05:21automatically one of these jobs
68. 05:25disappears and when you get your results back you get your job back
69. 05:29but keeping in mind that this is just a demo and anyway the
70. 05:35the qasm simulator will mimic the behaviour of an actual
71. 05:39device that's the one we're going to use right now it can simulate up
72. 05:43to thirty two Qubits so we're good in terms of the number of Qubits
73. 05:48and the other thing that we can select is the number of shots
74. 05:53so the number of shots it's how many times this will be repeated
75. 05:57because the result will be a probability distribution
76. 06:02and therefore we need to repeat the execution of the circuits many times
77. 06:06to estimate what's the probability of observing each of the states
78. 06:14so we are going to give it a name
79. 06:18and we will leave the default number of shots which is
80. 06:23one thousand and twenty four (1024)
81. 06:25and we will run it on our device
82. 06:32so now our job should appear here
83. 06:38in composer jobs it says it's already
84. 06:44finished and we can have a preview here
85. 06:49there are more details about the time it took how much the
86. 06:54different steps that were done first
87. 06:59the job was created and it was transpiled validated in queue and
88. 07:04then running
89. 07:07we can also check more details about what happened where it
90. 07:13was executed and when the number of shots the job id that identifies uniquely this concrete
91. 07:19job and then the result is shown in our histogram
92. 07:24so of these one thousand and twenty four shots we observe the one one (11)
93. 07:31state five hundred and fifteen (515) times and the zero zero (00) state
94. 07:37five hundred and nine (509) times and if we want to see it into
95. 07:41more detail we can also always come here and see the complete
96. 07:46information even the transpiled circuit which in this case it's
97. 07:52the same as the original circuit because
98. 07:56since we run it in the qasm simulator
99. 08:00the qasm simulator has basis gates both H and CNOT but if
100. 08:05we had run it in another Backend
101. 08:07the transpiled circuit would be different
102. 08:10you can also check the qasm code that is
103. 08:13equivalent to our experiment to the circuit that we created
104. 08:18and also how it would be done with Qiskit
105. 08:23okay so coming back to our composer tool
106. 08:29let's hide this and let's see what are the things we can explore
107. 08:35so in the view there is also other things that we can enable
108. 08:41first one is a code editor that appears here on the right and here we can
109. 08:46take directly as we create it i'm going for example delete this
110. 08:53so that you can see how it changes automatically and maybe add some
111. 08:59gates and as you can see they appeared here
112. 09:04and they give us the equivalent code in Qiskit or in OpenQASM
113. 09:09so depending on the kind of user that we are
114. 09:12or on the kind of experiment that we are doing at a concrete time
115. 09:16it might be interesting for us to have one code or the other
116. 09:24so what are the things can we check
117. 09:28we also have some of the
118. 09:31graphics that we can
119. 09:34explore so one is the Statevector that gives us
120. 09:38the amplitude - if we have a
121. 09:43measurement then it's before measurement, otherwise it will be after
122. 09:49so here we can see the actual amplitudes that then resulted
123. 09:53into the probability distribution that we observed
124. 09:56that we observed in the experiment
125. 10:02besides that it might be also interesting for us to see
126. 10:08what would be the probabilities
127. 10:11after measuring so this is also simulated here even before executing the experiment
128. 10:18so that we can also have an idea if we are doing what we are supposed to do
129. 10:23finally we also have
130. 10:26visualization which is the Q-sphere
131. 10:29that is the visualization we use when we have multiple Qubits
132. 10:33and it enables us to also understand
133. 10:38what's going to be the state after applying all these gates
134. 10:43and with that we conclude
135. 10:47we conclude the composer demo
136. 10:50there will be an exercise that you can do to get more
137. 10:55familiar with the platform and you are welcome to play around with it
138. 11:01keep and execute your first experiments in the quantum devices
139. 11:08so with that in the next video we're gonna move to the quantum
140. 11:13lab and to start coding with Qiskit
141. 11:16thank you so much for watching and looking forward to seeing
142. 11:18you in the next video

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