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Which subatomic particle does each company use in quantum computing?

Google, IBM and Rigetti use transmon qubits; these are basically fancy LC circuits where a Josephson junction and capacitor connect two superconducting islands. Because of this, they are also often ...
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Why do the IBM and Google processors both have 53 qubits?

It's just a coincidence. I can speak from personal recollection on the Google side. Google originally intended to use a 72 qubit chip (Bristlecone) where qubits were essentially directly connected to ...
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Accepted

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Location of "bad" qubits on Sycamore

Although it doesn't explicitly say it in the paper from Google, the diagrams in the paper are missing a qubit along the top edge. Most likely this is the "bad" qubit that wasn't used.
Accepted

Location of "bad" qubits on Sycamore

When I visited the Google Hardware Lab, they were extremely secretive about everything. It is unlikely anyone will be able to answer this question except for the narrow range of Google Hardware Lab ...

Quantum Supremacy: Some questions on cross-entropy benchmarking

That seems to restrict the output probability distributions of all quantum circuits to rather high entropy distributions. The output of a typical randomly chosen quantum circuit is rather high ...
• 21.9k
Accepted

Understanding Google's “Quantum supremacy using a programmable superconducting processor” (Part 1): choice of gate set

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 ...
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Fundamentally, a device such as an IBM quantum computer interacts according to a Hamiltonian, which might have some time-varying parameters. For example, for a single qubit, it might look like:  H=...
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Accepted

What did exactly Google do in simulating a random quantum circuit on a classical computer in supremacy experiment?

All quantum circuits can be simulated on a classical computer, but not all circuits take the same amount of time to simulate. If information about the circuit is known in advance, certain patterns may ...
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Accepted

Where are the physical gates in the Google processor?

In relating quantum computing to classical computing there may be a small conceptual hurdle that needs to be overcome. Although a classical $\mathsf{NAND}$ gate may be implemented in hardware (say ...
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Can we conclude that errors on Sycamore are Poisson-distributed Pauli errors?

The model's accuracy is purely empirical observation. The error trend (Fig 4, or 41:50 in the video) demonstrates that the error of the system (cross entropy fidelity with respect to simulated results)...
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How exactly is solving the random circuit sampling problem a computation in the Church-Turing thesis sense?

In the framing of the question (which I believe to be asked in good faith), there seems to be at least two objections. Sampling from a set of strings is not clearly a function, and Sampling is a ...
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How exactly is solving the random circuit sampling problem a computation in the Church-Turing thesis sense?

The Church-Turing thesis is not in and of itself a rigorous concept, but rather a judgment on rigorous concepts of computability. As such, it's negotiable. The language in Rosser's 1939 expository ...
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Quantum Supremacy: Some questions on cross-entropy benchmarking

After some further consideration I think it's quite clear that the only probability mass function evaluated in the computation of $\mathcal{F}_{\text{XEB}}$ is that of the classically computed ideal ...

What does Google's claim of "Quantum Supremacy" mean for the question of BQP vs BPP vs NP?

Paraphrasing some tweets on the matter earlier, the result is rather underwhelming because it plays on a discrepancy between what they mean by quantum supremacy (QS) and what people tend to think QS ...
Accepted

Do quantum supremacy experiments repeatedly apply the same random unitary?

Generally speaking, to prove quantum supremacy, you don't need to sample several times from the same unitary/circuit/output probability distribution. If you extract even a single sample from the ...
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Accepted

What determines the repetition rate in Google's Weber datasheet?

How is this repetition rate calculated? The repetition rate is how many samples can be collected per second. You compute it by collecting some large number of samples and checking how much time it ...
• 21.9k
Accepted

Can Google Sycamore's benchmark for quantum supremacy be simulated on Qiskit?

the benchmarking method used in this paper is called cross entropy benchmarking (XEB). An example circuit implementation for a 5 qubit XEB sequence is shown in fig. 3 of the paper. For further info, I ...
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Quantum Supremacy: Some questions on cross-entropy benchmarking

As an initial matter, I think the Supplementary Information (linked in some other answers on this sight) has a significant amount of discussion on $\mathcal{F}_{XEB}$. However, as I understand it (...
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Understanding Google's “Quantum supremacy using a programmable superconducting processor” (Part 1): choice of gate set

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 ...
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Do quantum supremacy experiments repeatedly apply the same random unitary?

In the Sycamore paper linked in the comments, in the description of FIG. 4, the authors state: ...For each $n$, each instance is sampled with $N_s$ between 0.5 M and 2.5 M... For $m=20$, obtaining 1M ...
• 6,787
Accepted

Why does Google's quantum processor outperform IBM's?

Both IBM and Google unveiled 53-qubit processors. At this time, only Google published performance metrics such as 1- and 2-qubit gate errors. Until IBM publishes similar metrics we simply cannot even ...
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