32
votes
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 ...
- 5,359
21
votes
Accepted
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 ...
- 33.3k
16
votes
Accepted
What does Google's claim of "Quantum Supremacy" mean for the question of BQP vs BPP vs NP?
Google's paper/results are kind of sideways to questions in computational complexity about the relation between $\mathrm{BPP}$ and $\mathrm{BQP}$ (and even further from questions about whether $\...
- 10.7k
8
votes
Accepted
Understanding Google's “Quantum supremacy using a programmable superconducting processor” (Part 3): sampling
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 ...
glS♦
- 23.3k
8
votes
Accepted
Understanding Google's “Quantum supremacy using a programmable superconducting processor” (Part 2): simplifiable and intractable tilings
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 ...
- 10.7k
7
votes
Accepted
Making sense of the Sycamore's computing prowess - power consumption
They say in Section X.H of the supplement that the Summit supercomputer has a power capacity of 14 megawatts. They compare that to their own setup. Their power consumption is mainly their dilution ...
- 1,251
7
votes
Accepted
Why Google has used $\sqrt{X}$ and $\sqrt{Y}$ instead of $X$ and $Y$ in supremacy experiment?
While Craig Gidney (from Google) is correct in his comment which says that $X$ and $Y$ do not create superpositions on states that are not in superposition, such as $|0\rangle$ and $|1\rangle$; even ...
- 13.5k
7
votes
Accepted
How are the IBM's and Google's Hadamard gates fabricated and operated?
A Hadamard gate isn't usually a physical object that you pass qubits through. In the case of superconducting qubits, the Hadamard gate is performed by bouncing microwaves off of the qubits. It doesn't ...
- 33.3k
7
votes
Sycamore 2 versus Osprey
One way you can compare Google's chips and IBM's chips is by computing detection fractions. Error correcting codes are built out of "detectors", which are sets of measurements with ...
- 33.3k
6
votes
Accepted
Do all physical architectures for quantum computers use the same universal gate sets?
So any universal gate set can replicate any other, since both are universal, but different architectures generally have different physical gates. While Clifford+T is a universal gate set that is very ...
- 1,766
6
votes
Accepted
What is the basic hardware gate library in the IBM & google?
IBM
You can view the basis gates that supporting at the hardware level for IBM's hardware through your dashboard. All the devices with more than 1 qubit have the same set of basis gates $\{CX, ID, RZ, ...
- 13.7k
4
votes
Accepted
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 ...
- 107
4
votes
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 ...
- 33.3k
4
votes
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 ...
- 10.7k
4
votes
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.
- 41
4
votes
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 ...
- 301
4
votes
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 ...
- 96
4
votes
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 ...
- 10.7k
4
votes
Accepted
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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4
votes
How are the IBM's and Google's Hadamard gates fabricated and operated?
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=...
- 55.7k
3
votes
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 ...
- 10.7k
3
votes
Accepted
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 ...
- 1,251
3
votes
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 ...
3
votes
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 ...
- 388
3
votes
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 ...
- 899
3
votes
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 ...
glS♦
- 23.3k
3
votes
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 ...
- 33.3k
3
votes
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 ...
- 1,190
3
votes
Accepted
Status of Google's quantum supremacy claim 2022
The paper simulating the random circuit sampling task was published in PRL. An even larger scale simulation verified the 53 qubit, 20 cycle Google results directly. RE repeating the experiments, ...
- 623
3
votes
Publicly available samples for quantum circuits and/or simulators
This isn't really a NISQ circuit, but it's certainly run on a NISQ machine and it does include samples with circuits. The data from "Suppressing quantum errors by scaling a surface code logical ...
- 33.3k
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