User Craig Gidney

29 votes

Are there emulators for quantum computers?

emulation

answered Mar 12, 2018 at 23:21

24 votes

How does a quantum computer do basic math at the hardware level?

architecture physical-realization superconducting-quantum-computing

answered Apr 10, 2018 at 17:54

23 votes

Accepted

Is quantum computing mature enough for a computer scientist with no physics background?

resource-request

answered Aug 8, 2018 at 1:26

23 votes

Can the Bloch sphere be generalized to two qubits?

resource-request bloch-sphere state-space-geometry

answered Nov 13, 2018 at 23:42

22 votes

Accepted

Are circuits with more than 1000 gates common?

quantum-gate classical-computing

answered May 31, 2021 at 21:14

19 votes

Why do the IBM and Google processors both have 53 qubits?

physical-qubit quantum-advantage ibm google-sycamore

answered Nov 4, 2019 at 21:44

16 votes

What is the opposite of measurement, in a quantum circuit?

quantum-gate measurement

answered Feb 7, 2020 at 20:28

14 votes

Accepted

Why are quantum gates unitary and not special unitary?

quantum-gate unitarity

answered May 13, 2018 at 5:23

14 votes

Is Qiskit more popular than cirq? Why?

qiskit cirq

answered Jul 30, 2021 at 20:48

13 votes

Are quantum computers just a variant on Analog computers of the 50's & 60's that many have never seen nor used?

classical-computing programming adiabatic-model technologies

answered Jul 8, 2018 at 17:47

12 votes

What are physically allowed CNOTs for Rigetti's 19 qubit chip and Google's 72 qubit BristleCone chip?

bristlecone rigetti cirq

answered Jul 19, 2018 at 17:55

12 votes

The algorithm of the new quantum factoring record 1,099,551,473,989

algorithm

answered Dec 14, 2019 at 22:29

11 votes

How to think about the Z gate in a Bloch sphere?

quantum-gate bloch-sphere

answered Jun 2, 2018 at 1:03

11 votes

Accepted

How to implement the "Square root of Swap gate" on the IBM Q (composer)?

quantum-gate gate-synthesis ibm-q-experience

answered Jun 4, 2018 at 22:42

11 votes

Accepted

Quantum advantage with only Clifford gates (Gottesman Knill theorem)

algorithm complexity-theory quantum-advantage stabilizer-state

answered Oct 10, 2021 at 16:30

10 votes

Accepted

Can a Toffoli gate be implemented using Fredkin gates?

circuit-construction universal-gates

answered Dec 27, 2019 at 17:50

9 votes

Accepted

Why does measuring one qubit after the other in this entangled system alter the result?

quantum-state entanglement measurement

answered Dec 7, 2019 at 19:56

9 votes

Accepted

Nielsen and Chuang, Exercise 6.5: How to simulate oracle for n+1 qubits using one oracle gate for n qubits and one extra qubit?

grovers-algorithm nielsen-and-chuang oracles

answered Dec 25, 2019 at 12:31

9 votes

Why should we use inverse QFT instead of QFT in Shor's algorithm?

algorithm shors-algorithm quantum-fourier-transform

answered Jun 9, 2019 at 19:59

9 votes

Accepted

What is the minimum integer value to make quantum factorization to be worthwhile?

algorithm speedup

answered Apr 17, 2018 at 18:38

9 votes

Accepted

Obtaining gate $e^{-i\Delta t Z}$ from elementary gates

quantum-gate gate-synthesis simulation hamiltonian-simulation pauli-gates

answered Apr 22, 2018 at 17:42

9 votes

Accepted

Is there a classical limit to quantum computing?

measurement decoherence ion-trap-quantum-computing

answered Sep 5, 2018 at 15:02

9 votes

Accepted

Approximating unitary matrices

quantum-gate gate-synthesis solovay-kitaev-algorithm

answered Dec 27, 2018 at 15:58

9 votes

Procedures and intuition for designing simple quantum circuits?

circuit-construction nielsen-and-chuang textbook-and-exercises

answered Jun 12, 2020 at 21:37

9 votes

How do I check if a gate represented by Unitary $U$ is a Clifford Gate?

algorithm complexity-theory clifford-group

answered Aug 3, 2020 at 17:31

9 votes

Is there any difference between "value of a qubit" and its "state"?

quantum-state textbook-and-exercises notation terminology

answered Mar 17, 2021 at 15:30

9 votes

If two unitary operators commute, do their roots also commute?

circuit-construction mathematics quantum-fourier-transform

answered Feb 24 at 18:57

9 votes

Accepted

Building a controlled NOT gate which is controlled by the qubit it is acting on

quantum-circuit

answered Aug 11 at 16:33

8 votes

Accepted

Why doesn't Shor's algorithm output a solution for some numbers?

qiskit shors-algorithm period-finding-algorithm

answered May 15 at 16:57

8 votes

Accepted

Is the SWAP gate a Clifford Gate? How would I express it using the Clifford Gate generators?

qiskit quantum-gate textbook-and-exercises simulation clifford-group

answered Nov 11, 2021 at 18:04

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476 Answers

Are there emulators for quantum computers?

How does a quantum computer do basic math at the hardware level?

Is quantum computing mature enough for a computer scientist with no physics background?

Can the Bloch sphere be generalized to two qubits?

Are circuits with more than 1000 gates common?

Why do the IBM and Google processors both have 53 qubits?

What is the opposite of measurement, in a quantum circuit?

Why are quantum gates unitary and not special unitary?

Is Qiskit more popular than cirq? Why?

Are quantum computers just a variant on Analog computers of the 50's & 60's that many have never seen nor used?

What are physically allowed CNOTs for Rigetti's 19 qubit chip and Google's 72 qubit BristleCone chip?

The algorithm of the new quantum factoring record 1,099,551,473,989

How to think about the Z gate in a Bloch sphere?

How to implement the "Square root of Swap gate" on the IBM Q (composer)?

Quantum advantage with only Clifford gates (Gottesman Knill theorem)

Can a Toffoli gate be implemented using Fredkin gates?

Why does measuring one qubit after the other in this entangled system alter the result?

Nielsen and Chuang, Exercise 6.5: How to simulate oracle for n+1 qubits using one oracle gate for n qubits and one extra qubit?

Why should we use inverse QFT instead of QFT in Shor's algorithm?

What is the minimum integer value to make quantum factorization to be worthwhile?

Obtaining gate $e^{-i\Delta t Z}$ from elementary gates

Is there a classical limit to quantum computing?

Approximating unitary matrices

Procedures and intuition for designing simple quantum circuits?

How do I check if a gate represented by Unitary $U$ is a Clifford Gate?

Is there any difference between "value of a qubit" and its "state"?

If two unitary operators commute, do their roots also commute?

Building a controlled NOT gate which is controlled by the qubit it is acting on

Why doesn't Shor's algorithm output a solution for some numbers?

Is the SWAP gate a Clifford Gate? How would I express it using the Clifford Gate generators?