26 If all quantum gates must be unitary, what about measurement? 2018-03-15T15:02:47.357

16 If quantum gates are reversible how can they possibly perform irreversible classical AND and OR operations? 2018-03-15T10:58:34.123

16 Quantum states are unit vectors... with respect to which norm? 2018-07-13T11:43:57.257

14 Why are quantum gates unitary and not special unitary? 2018-05-12T21:57:48.573

12 What do they mean by "qubit can't be copied"? 2018-09-12T20:52:53.267

11 Implementing "Classical AND Gate" and "Classical OR Gate" with a quantum circuit 2019-04-01T15:04:55.907

8 How to check if a quantum circuit can be constructed for a given matrix representation? 2021-02-02T20:10:28.237

7 What is the probability $\Pr(||U-I||_{op}<\varepsilon)$ of a Haar-random unitary being close to the identity? 2020-08-12T19:51:12.293

7 Does the no-hiding theorem suggest that quantum information is never destroyed? 2021-01-28T01:13:28.310

6 What is the smallest quantum circuit to produce two-qubit state (a,b,b,b)? 2018-08-27T13:54:31.473

6 General parametrisation of an arbitrary $2\times 2$ unitary matrix? 2019-01-14T08:32:50.917

6 How to prove that the query oracle is unitary? 2019-03-26T12:11:16.280

6 Can the Kraus decomposition always be chosen to be a statistical mixture of unitary evolutions? 2019-08-06T16:15:21.107

6 Is there a quantum operation whose output is always orthogonal to the input? 2019-10-03T08:19:37.670

6 Is the Haar measure invariant under conjugation? 2020-09-06T00:18:31.727

5 Extending a square matrix to a unitary matrix 2019-01-10T10:26:05.743

5 What are the constraints on a matrix that allow it to be "extended" into a unitary? 2019-01-10T12:22:28.853

5 Finding a global phase that transform the Hadamard gate to an element of $SU(2)$ and propose an evoultion operator which implents the operation 2019-07-18T23:17:31.373

5 Explicit form for composition of Choi representation quantum channels 2020-03-08T21:30:50.937

5 How can I fill a unitary knowing only its first column? 2020-03-20T05:38:59.657

4 Unitary gate(s) from product of exponent 2018-11-26T07:15:35.667

4 Understanding why the modular function part of Shor's algorithm is unitary 2018-12-14T12:21:31.490

4 Differentiate between local and global unitaries 2019-03-01T07:03:38.450

4 What is the unitary operator realizing a given CPTP operator 2019-07-31T22:59:33.860

4 Prove that the state $\sum_{S\in P_n}(-)^{\tau(S)}|S\rangle$ is invariant up to a phase when changing the basis 2019-11-28T05:29:26.923

4 What unitary gate produces these quantum states from the computational basis? 2020-01-08T18:50:07.887

4 What is the correct sign in the unitary evolution operator of a beam splitter? 2020-03-03T15:10:32.627

4 How should I understand the change of qubit's basis as a rotation? 2020-03-14T12:06:08.600

4 Unitary over bipartite states that can turn a non-product state into a product state 2020-12-19T20:14:30.060

4 Is the column vector of a uniformly sampled random unitary matrix a uniformly sampled random state vector? 2021-01-18T23:00:36.327

3 Unitary acting on standard qubit basis properties 2018-10-27T20:21:45.527

3 What do you specify when you physically apply a unitary? 2019-01-13T12:50:38.063

3 Bipartite states whose coefficients are entries of a unitary matrix 2020-06-03T21:16:51.567

3 How do you embed a POVM matrix in a Unitary? 2020-07-05T08:09:11.263

3 Representing a von Neumann measurement as $[\mathcal{I} \otimes P_i] U(\rho_s \otimes \rho_a)U^{-1} [\mathcal{I} \otimes P_i]$, how do we choose $U$? 2020-07-15T14:43:17.730

3 Can we always find a unitary operation connecting qubit states with given eigendecompositions? 2020-08-22T13:40:22.413

3 How to find the unitary operation of a depolarizing channel? 2020-09-01T16:18:02.667

3 How does one create the unitary sending $|0\rangle$ into a target quantum state? 2021-02-03T07:09:15.167

2 Are CPTP operators and unitary operators the same thing? 2019-07-31T15:59:14.833

2 Does the general form of a unitary operator define strict signs for the second column? 2019-08-17T06:46:21.323

2 Find the local unitary that takes the bell state to a state phi that has an extractable bell state 2019-08-22T22:18:50.613

2 Are there different orderings of the fifteen SU(4) generators in common use? 2020-01-19T15:35:10.877

2 How to prove that a matrix is an arbitrary unitary? 2020-03-19T10:20:12.647

2 Is $e^{i\beta} R_Z(-2\beta)$ equivalent to $U_1(2\beta)$? 2020-06-10T12:39:01.233

2 Nielsen & Chuang Theorem 2.6 Proof 2020-08-26T14:12:44.430

2 How can I convert the unitary matrix $e^\frac{i\pi}{2}$ into a quantum circuit in Qiskit? 2020-09-16T14:35:08.213

2 Can the (universal) state inversion operator be physically realized? 2020-11-11T18:31:48.380

2 What is $\sum_{i}\langle i \vert U \vert j\rangle$ for unitary $U$? 2020-11-24T21:50:11.403

2 A question about Grover's paper "Fixed-Point Quantum Search" 2020-12-07T20:05:44.030

2 How to find the output state after evolution through a unitary? 2021-01-01T04:12:55.297

2 How to prepare a random 1-qubit superposition for data encoding 2021-02-26T18:29:22.523

1 Is it correct to say that we need controlled gates because unitary matrices are reversible? 2019-02-07T19:05:03.013

1 How can classical computations be non-unitary? 2019-10-02T22:17:14.487

1 Trying to make irreversable operation in the quantum circuit 2019-11-12T16:44:23.017

1 Circuit of a very trivial thing 2020-02-22T20:24:22.820

1 Initial assumption of the unitary that allows us to estimate the label function 2020-06-01T18:48:15.453

1 Hadamard gate for three qubits; inconsistency between IBM and Matlab 2020-09-16T22:57:20.080

1 What are the physical meanings of the outer product when writing expressions for unitary gates? 2020-11-01T04:29:58.150

1 How to perform the unitary transformation $U|i,j_1\rangle = 1/\sqrt{k}(|i,j_1\rangle+|i,j_2\rangle+|i,j_3\rangle...+|i,j_k\rangle)$? 2020-11-20T05:24:02.787

1 How to apply a operator to qubit system on the basis of current state of system? 2020-11-22T16:06:09.377

0 Should a Pauli $X$ matrix equal the identity matrix to be unitary? 2019-09-09T18:40:51.597

0 How can I build up an arbitrary quantum circuit given a certain unitary matrix operation? 2020-01-20T14:15:06.057

0 Could someone give an example of this pic? 2020-04-12T01:21:55.047

0 Find the decomposition of the following matrix into two level unitary matrices 2020-05-04T08:24:11.747

0 Convert a two-ququart (16 x 16) density matrix into normal form--so that the components of the Bloch vectors of the two reduced systems are all zero 2020-06-22T18:01:52.960

0 How to force a matrix to be unitary given constraints on some of the elements? 2020-10-15T23:49:56.257

0 What is the effect of the reset gate on the matrix form of a gate/circuit? 2020-11-17T08:09:52.177

0 Creating a parameterized Operator in Qiskit 2020-11-27T14:44:38.970

0 Compiling Quantum Circuits using the Palindrome Transform 2021-02-05T00:55:15.780

0 Find the unitary implementing the transformation $|0\rangle\to\frac1{\sqrt2}(|0\rangle+|1\rangle),|1\rangle\to\frac1{\sqrt2}(|0\rangle-|1\rangle)$ 2021-02-11T06:09:27.660

0 3-qubit phase shift gate/circuit implementation without any Ancilla qubits 2021-02-27T07:26:03.030

-1 Why is a Hadamard gate unitary? 2020-01-03T08:24:55.260