7

What does "obtaining samples" mean in this context? The same thing it means in a more classical context. Consider the probability distribution of the possible outcomes of a (possibly biased) coin flip. Sampling from this probability distributions means to flip the coin once and record the result (head or tail). If you sample many times, you can retrieve ...


7

TL/DR: The two-qubit gates are going by the moniker "Sycamore gates" in the paper, and it appears that they would ideally want to explore more of the $(\phi, \theta)$ phase-space but for their purposes (of quantum supremacy) their current Sycamore gate is sufficient. The pattern of gates $\mathrm{ABCDCDAB}$ was chosen to avoid "wedges" ...


4

While a follow-up question asks for the motivation behind the two-qubit gates used in Sycamore, this question focuses on the random nature of the single qubit operations used in Sycamore, that is, the gates $\{\sqrt{X},\sqrt{Y},\sqrt{W}=(X+Y)/\sqrt{2}\}$ applied to each of the $53$ qubits between each of the two-qubit gates. Although I agree with @Marsl ...


3

By coincidence, this article just came out on Ars Technica which might answer some of your questions. (This is not an endorsement of everything written in that article. But the author basically asked, and researched, the same question that you're asking.) The TL;DR answer is that superconducting qubits are manufactured and allow for better control over ...


2

This answer only addresses the part about the necessity of the randomness of the circuit because I am by no means familiar with the physical implementation of the qubits at Google and what kind of constraints these impose on the implementation of certain gates. Now, for the randomness: Consider the problem of sampling from the output distribution of a ...


1

Distinguishing $X$ and $Z$ errors is easy. $X$ errors anti-commute with the $Z$-type stabilizers, and so when you perform a measurement of those parity checks, you get and answer '1'. Similarly, $Z$ errors give you a '1' answer only on the $X$-type parity checks. Also, note that, in the bulk (i.e. not on the edges), you never get a '1' on only one weight-4 ...


1

They are resources to help people get started with learning about quantum computing. They are also useful to help further research as services such as IBM Q Experience provide access to real quantum computers, and so people can conduct research using them.


1

Not sure if this answers your question directly, but Docplex, which is IBM's Decision Optimization CPLEX Modeling for Python is capable of generating an Ising hamiltonian from a cost function. Take a look at this qiskit tutorial.


1

According to [1]: Readout error is the error in measuring qubits. You read the figure correctly (44 out of 1000 measurements fail on reading). Note there is yet another, though minor, error there: gate error. It is about errors in quantum gate operation, and is one 10th less than the error of measurement. So, actually there may occur more erroreus ...


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