User Craig Gidney

133 votes

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In a roller coaster, does the rear car have a higher acceleration/speed?

answered Oct 9, 2017 at 17:32

12 votes

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Delayed Choice Quantum Eraser: Am I missing something here?

quantum-mechanics quantum-entanglement double-slit-experiment quantum-eraser

answered Oct 27, 2015 at 17:17

10 votes

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quantum clone of orthogonal quantum states

quantum-mechanics quantum-information

answered May 3, 2016 at 20:44

10 votes

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Why do quantum gates have to be reversible?

quantum-information quantum-computer unitarity

answered Jul 28, 2016 at 8:04

10 votes

Quantum circuit for a $3$-qubit $|W \rangle$ state

hilbert-space quantum-information quantum-entanglement quantum-computer

answered Feb 13, 2017 at 15:48

9 votes

How do we imagine a Hadamard gate acting on the Bloch Sphere?

quantum-mechanics quantum-information quantum-computer

answered Jan 10, 2016 at 2:56

8 votes

Visual interpretation, on the Bloch sphere, when Hadamard gate is applied twice

quantum-mechanics quantum-information bloch-sphere

answered Jun 12, 2017 at 1:25

7 votes

Will quantum computing provide any advantage for storing large amounts of data?

quantum-computer data

answered Sep 22, 2017 at 22:24

7 votes

Is the partial trace of a mixed state always mixed? If not, are there natural examples where the partial trace of a mixed state is a pure state?

quantum-information density-operator quantum-states

answered Dec 7, 2017 at 18:26

7 votes

What is quantum about the no-cloning theorem?

quantum-mechanics classical-mechanics hamiltonian-formalism

answered Dec 5, 2016 at 6:18

7 votes

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How is quantum teleportation any better than regular transfer of information?

quantum-mechanics quantum-information quantum-teleportation

answered Jul 13, 2017 at 14:27

7 votes

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Quantum Grover's algorithm: constructing the black box gate

quantum-computer algorithms

answered Apr 22, 2016 at 16:13

7 votes

Double slit experiment; evidence of wavefunction collapse

quantum-mechanics double-slit-experiment wavefunction-collapse

answered Jun 19, 2016 at 3:07

7 votes

Complexity of quantum simulation

quantum-information

answered Apr 28, 2016 at 16:00

6 votes

Accepted

How does quantum superposition make calculation faster?

quantum-information quantum-computer superposition

answered May 5, 2016 at 17:40

6 votes

Are the 'clock' and 'shift' operators used in Qudit codes physically realizable?

quantum-mechanics quantum-information quantum-spin quantum-computer

answered Jun 10, 2016 at 21:29

6 votes

How can a quantum logic gate produce a value other than $0$ or $1$?

quantum-mechanics quantum-information quantum-computer

answered Jul 19, 2016 at 17:45

6 votes

What is the use of a Universal-NOT gate?

quantum-mechanics quantum-information research-level quantum-computer

answered Apr 3, 2016 at 18:12

6 votes

Shor's algorithm - why doesn't the final collapse of the auxiliary qubits cripple the computation?

quantum-mechanics quantum-information causality algorithms

answered Nov 19, 2017 at 4:10

5 votes

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Parity Measurement Using a Single c-Z gate

quantum-mechanics quantum-information quantum-computer

answered Apr 14, 2017 at 14:45

5 votes

Why does the distributive law fail in quantum logic?

quantum-mechanics quantum-information

answered Feb 25, 2017 at 7:12

5 votes

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How can all information be localized if local realism is dead?

quantum-mechanics quantum-information quantum-interpretations

answered Mar 7, 2016 at 19:46

5 votes

Why is a two-qubit state described by a point in a 15-dimensional space?

quantum-mechanics hilbert-space quantum-computer density-operator quantum-states

answered Apr 13, 2016 at 18:04

5 votes

Can every density operator be written as an outer product of two vectors?

quantum-mechanics quantum-information hilbert-space density-operator

answered May 26, 2016 at 16:02

4 votes

Invariance of a maximally entangled state under unitary operation $U \otimes U^\dagger$

quantum-mechanics homework-and-exercises quantum-information quantum-entanglement

answered Jul 28, 2016 at 15:35

4 votes

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Is QC with Superpositioned Quantum Gates any different than normal Quantum Computation?

quantum-mechanics quantum-information quantum-computer superposition

answered Apr 9, 2016 at 7:35

4 votes

Why is $\theta \over 2$ used for a Bloch sphere instead of $\theta$?

quantum-information hilbert-space group-theory representation-theory bloch-sphere

answered Dec 16, 2016 at 23:45

4 votes

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Simulating Toffoli Gates with Fredkin Gates with no garbage bits

quantum-information quantum-computer

answered Aug 2, 2017 at 17:18

4 votes

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Delayed Choice Quantum Eraser without retrocausality?

quantum-mechanics quantum-information quantum-eraser

answered Jul 10, 2017 at 17:23

3 votes

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If ABR is a pure state, why S(A,B) = S(R), where S is the Von Neumann entropy?

quantum-mechanics homework-and-exercises quantum-information entropy entanglement-entropy

answered Jan 5, 2018 at 3:22

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139 Answers

In a roller coaster, does the rear car have a higher acceleration/speed?

Delayed Choice Quantum Eraser: Am I missing something here?

quantum clone of orthogonal quantum states

Why do quantum gates have to be reversible?

Quantum circuit for a $3$-qubit $|W \rangle$ state

How do we imagine a Hadamard gate acting on the Bloch Sphere?

Visual interpretation, on the Bloch sphere, when Hadamard gate is applied twice

Will quantum computing provide any advantage for storing large amounts of data?

Is the partial trace of a mixed state always mixed? If not, are there natural examples where the partial trace of a mixed state is a pure state?

What is quantum about the no-cloning theorem?

How is quantum teleportation any better than regular transfer of information?

Quantum Grover's algorithm: constructing the black box gate

Double slit experiment; evidence of wavefunction collapse

Complexity of quantum simulation

How does quantum superposition make calculation faster?

Are the 'clock' and 'shift' operators used in Qudit codes physically realizable?

How can a quantum logic gate produce a value other than $0$ or $1$?

What is the use of a Universal-NOT gate?

Shor's algorithm - why doesn't the final collapse of the auxiliary qubits cripple the computation?

Parity Measurement Using a Single c-Z gate

Why does the distributive law fail in quantum logic?

How can all information be localized if local realism is dead?

Why is a two-qubit state described by a point in a 15-dimensional space?

Can every density operator be written as an outer product of two vectors?

Invariance of a maximally entangled state under unitary operation $U \otimes U^\dagger$

Is QC with Superpositioned Quantum Gates any different than normal Quantum Computation?

Why is $\theta \over 2$ used for a Bloch sphere instead of $\theta$?

Simulating Toffoli Gates with Fredkin Gates with no garbage bits

Delayed Choice Quantum Eraser without retrocausality?

If ABR is a pure state, why S(A,B) = S(R), where S is the Von Neumann entropy?