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Programming Quantum Computers: Errata

This document contains information about errors we've identified in the book's first edition. If you have more, please feel free to contact us via email or by logging a Github issue! Many thanks from EJ, Nic and Mercedes.

Table 2-2

Thanks to Haeil Yi for pointing this out! The value 0.35 in the fourth row of the table should be 0.31

Example 2-3

Thanks to checky2010 (Jonas) for pointing this out! The sign of the phase(90) operation doesn't match the sign of the online example phase -90. This is also an issue in Figure 2-16 and Figure 2-18. Might be good to add a note that the operation works eiother way, so long as you're consistent.

Page 32: Spy Hunter

Thanks to Mariia at Microsoft for pointing out this one, and to Cláudio Gomes at Universidade de Coimbra for additional correction!

Incorrect: "Any spy who tries to read one of these qubits has a 25% chance of getting caught. So even if Alice and Bob only use 50 of them in the whole transfer, the spy’s chances of getting away are far less than one in a million."

Corrected: "Any spy who tries to read one of these qubits has a 12.5% chance of getting caught. So even if Alice and Bob only use 100 of them in the whole transfer, the spy’s chances of getting away are close to one in a million."

Page 28: QPU Instruction: PHASE(θ)

Thanks to Dr. Moez AbdelGawad at Rice University for spotting this!

Incorrect: "These four states will be used in Example 2-4"

Corrected: "Some of these states will be used in Example 2-4"

Page 35: Spy Hunter

Thanks to Dr. Moez AbdelGawad at Rice University for spotting this!

Incorrect: "She sets it to value, ..."

Corrected: "She sets it to send_val, ..."

Page 40: Drawing a Multi-Qubit Register

Thanks to Dr. Moez AbdelGawad at Rice University for spotting this!

Incorrect: "... the random eight-qubyte circuit ..."

Corrected: "... the random eight-qubit circuit ..."

Comment in Example 3-4: The Swap Test

Thanks to Ilya Krepky for spotting this

Unclear: The output register is 1 only if inputs are equal

Better: The output register has probability 1 only if inputs are equal

Text for Example 3-6: Hands-on: Remote-Controlled Randomness

Thanks to Dr. Moez AbdelGawad at Rice University and Angelica Semenec for spotting this!

Text discussing Example 3-6 first, correctly, mentions the probabilities are 85%/15%, but then later, incorrectly, mentions the probabilities are 70%/30% and sticks to these figures. Luckily, the code in the book and online sticks to the correct 85%/15% probabilities.

Incorrect: "70%/30%"

Corrected: "85%/15%"

Page 79: Teleportation

Thanks to Shawn Bayern at Florida State University College of Law for spotting this one!

Incorrect: Bob always performs both a HAD and a PHASE(180) on his qubit

Corrected: Bob always performs both a NOT and a PHASE(180) on his qubit

Page 157: Eigenphases Teach Us Something Useful

Incorrect: Take careful of note how HAD acts on these states.

Corrected: Take careful note of how HAD acts on these states.

Figure 3-16

Thanks to Nomad on Amazon and also @toshaf and @dyordan1 for pointing out this one.

Incorrect:

Corrected:

Figure 3-28 Caption:

Thanks to Dr. Moez AbdelGawad at Rice University for spotting this!

Incorrect: "Walthrough of the constructed CPHASE operation"

Corrected: "Walkthrough of the constructed CPHASE operation"

Page 87: Arithmetic on a QPU

Thanks to Dr. Moez AbdelGawad at Rice University for spotting this!

Incorrect: "(a single gate which performs NOT(b AND b))"

Corrected: "(a single gate which performs NOT(a AND b))"

Teleportation Example 4-1 and Figure 4-4

Thanks to Fabio Salvi for spotting this!

Issue: It looks like the IBM QX system has changed since the book's publication, and the example may no longer run as written. Changing the OpenQASM sample to match the QCEngine sample, or alternatively using the Qiskit version solves the problem, but the OpenQASM version should be revisited and updated.

Figure 7-6

Thanks to Cláudio Gomes at Universidade de Coimbra for pointing out this one in Github issue #15!

In Figure 7-6, the final column was accidentally cropped out, so there were only 15 columns instead of 16.

Incorrect:

Corrected:

Figure 7-10 and surrounding text

Thanks to Dr. Joshua Guerin at The University of Tennessee at Martin for pointing out this one in Github issue #47!

In Figure 7-10, the 256-sample sine wave shown contains 6 cycles, but the text and labels refer to it as a one-second sample at 8Hz. As Figure 7-11 contains "a few more examples" including one at 8Hz, the best correction here is to adjust the text and labels for Figure 7-10 to 6Hz.

Incorrect:

Corrected:

Incorrect:

The DFT has transformed the signal into frequency space, where we can see all the frequency components present inside a signal. Since the input signal completes eight full oscillations within the sample time (1s), we expect it to have a frequency of 8 Hz, and this is precisely what the DFT returns to us in the output register.

Real and Complex DFT Inputs Looking at our example DFT output, you may notice the 248 Hz elephant in the room. Alongside the expected 8 Hz frequency, the DFT also produces a conspicuous second mirror-image peak in frequency space.

This is a property of the DFT of any real signal (one where the samples are all real numbers, as is the case for most conventional signals). In such cases, only the first half of the DFT result is actually useful. So in our example, we should only take note of the first 256/2 = 128 points that the DFT returns. Everything else in the DFT after that point will be the mirror image of the first half (which is why we see the second peak symmetrically at 256 – 8 = 248 Hz). Figure 7-11 shows a few more examples of the DFTs of real signals, further highlighting this symmetry.

Corrected:

The DFT has transformed the signal into frequency space, where we can see all the frequency components present inside a signal. Since the input signal completes six full oscillations within the sample time (1s), we expect it to have a frequency of 6 Hz, and this is precisely what the DFT returns to us in the output register.

Real and Complex DFT Inputs Looking at our example DFT output, you may notice the 250 Hz elephant in the room. Alongside the expected 6 Hz frequency, the DFT also produces a conspicuous second mirror-image peak in frequency space.

This is a property of the DFT of any real signal (one where the samples are all real numbers, as is the case for most conventional signals). In such cases, only the first half of the DFT result is actually useful. So in our example, we should only take note of the first 256/2 = 128 points that the DFT returns. Everything else in the DFT after that point will be the mirror image of the first half (which is why we see the second peak symmetrically at 256 – 6 = 250 Hz). Figure 7-11 shows a few more examples of the DFTs of real signals, further highlighting this symmetry.

Figure 8-8

Thanks to Greg Byrd from NC State University for pointing out this one in Github issue #32!

Issue: In Figure 8-8 and the relating text, "invQFT" should be "QFT".

Figure 9-2

Thanks to Mariia at Microsoft for pointing out this one!

The address lines in the image are drawn MSB-at-top instead of LSB-at-top, which is inconsistent with the data lines, and with Figure 9-4.

Incorrect:

Corrected:

**(Unconfirmed error reports are below)**

Figure 3-14 (unconfirmed)

Nomad on Amazon indicated Figure 3-16 contains an error.

EJ: I've been unable to spot the issue; it looks correct.