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

24 How does measurement of one qubit affect the others? 2018-03-19T16:31:15.507

20 How can I build a circuit to generate an equal superposition of 3 outcomes for 2 qubits? 2018-06-12T09:48:37.680

14 What makes quantum computations different from randomized classical computations? 2018-03-20T07:41:17.380

14 Representation of real numbers in quantum computers 2018-03-24T23:57:37.393

14 Do multi-qubit measurements make a difference in quantum circuits? 2018-04-04T10:49:17.640

14 What does "measurement in a certain basis" mean? 2018-04-22T15:43:42.417

12 What is the opposite of measurement, in a quantum circuit? 2020-02-07T18:38:19.103

11 What is the Helstrom measurement? 2018-09-05T14:59:27.757

10 Are true Projective Measurements possible experimentally? 2018-04-30T04:17:42.940

10 Density matrix after measurement on density matrix 2018-11-30T17:55:57.293

9 Optimal strategy to a quantum state game 2019-01-27T22:55:35.543

8 What does it mean to "measure an operator"? 2020-12-09T01:20:52.837

7 Does Barkhausen noise affect the measurement of magnetic particle based qubits? 2018-03-26T02:22:40.907

7 Is it true that observing a quantum state will end the superposition of states? How can I not observe? 2018-04-21T20:29:23.433

7 Measuring in standard basis meaning 2018-06-11T15:16:39.920

7 Is there a classical limit to quantum computing? 2018-09-05T10:23:49.770

7 Quantum channel representation of projective measurement 2019-06-13T00:57:22.930

7 How to compute the measurement probability in swap test? 2020-10-19T03:54:19.127

7 What can I conclude about $\langle \phi|\pi_1\pi_2|\phi\rangle$ if $\langle \phi|\pi_i|\phi\rangle\ge e$? 2020-11-17T17:06:58.183

7 If quantum computing always return random measurement (or uncertain measurement), why do we still need it? 2021-01-25T15:35:38.043

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

7 What do the off-diagonal elements of a density matrix physically represent? 2021-02-01T21:59:07.907

6 Projective measurements: aftermath and restoration 2018-05-20T07:48:47.487

6 Rank of a measurement 2018-05-30T15:29:35.763

6 Use of change of phase gates 2018-06-24T08:49:03.517

6 Reverse Quantum Computing: How to unmeasure a qunit 2018-06-29T15:24:57.843

6 Does the need of many quantum algorithms to be repeated several times impair the efficiency gains? 2018-08-09T09:34:48.640

6 Can one ever find the elements of a superposition state? 2018-11-08T18:51:27.320

6 Measuring qubits in QuTiP 2018-12-18T14:46:39.070

6 Do weak measurements (with/without weak values) have any application in quantum computation? 2019-01-28T16:06:21.193

6 Why is the application of an oracle function not a measurement? 2019-06-02T08:09:09.080

6 $n$ qubit vs. a $d=2^n$ qudit states and measurements 2019-06-17T14:32:27.537

6 How to calculate an Expected Value of some operator acting on qubits? 2019-08-04T12:05:06.087

6 Implementation of filter operation 2019-08-06T10:59:57.667

6 Why does a controlled gate not constitute a measurement? 2019-10-19T08:30:19.263

6 Circuit for VQE Expectation Value Finding 2020-09-08T16:31:47.587

6 Are perfectly LOCC-indistinguishable states necessarily identical? 2020-10-06T13:29:08.737

6 Trying to understand this measurement of a simple quantum circuit 2020-12-10T01:53:07.100

6 Distinguishing collapsed and uncertain qubit in a quantum circuit 2021-01-18T06:06:13.027

5 Are there any experimental groups currently measuring quantum contextuality? 2018-03-14T23:47:44.023

5 Accessible information of system vs system, apparatus and environment 2018-04-27T17:53:00.170

5 How to check states? 2018-06-29T10:04:47.453

5 What are the standard eigenvalues in $\mathbb{C^2}\otimes\mathbb{C^2}$? 2018-06-29T14:15:00.067

5 Fault tolerant quantum measurement: how is implemented the "majority vote" 2018-10-04T06:08:50.777

5 Is qubit superposition a basis-dependent concept? 2019-01-13T22:45:49.953

5 Where does the Xmon simulator from Googles cirq framework its entropy from? 2019-02-02T20:58:53.027

5 Why can't a quantum computer strongly simulate itself? 2019-03-31T11:14:57.570

5 What is an example of a measurement that is LOCC but not separable? 2019-04-02T20:48:06.680

5 Understanding a quantum algorithm to estimate inner products 2019-06-05T00:30:29.103

5 Why does measuring one qubit after the other in this entangled system alter the result? 2019-12-07T19:14:44.567

5 Projective vs general measurements - a missing piece 2020-06-01T17:18:24.840

5 How many samples are required to estimate the probabilities of a state? 2020-06-14T15:24:25.540

5 Prove that Shannon and von Neumann entropies satisfy $H(P)\ge S(\rho)$ with $P$ diagonal of $\rho$ 2020-09-05T14:36:45.233

5 Can I partially collapse the wavefunction in Qiskit? 2020-10-27T18:27:08.487

5 Are there any algorithms that take measurements in an intermediate step? 2020-12-31T17:13:02.470

5 What does $M_m |\psi_i\rangle$ mean in the equation $p(m|i)=\langle\psi_i|M_m^\dagger M_m|\psi_i\rangle$? 2021-01-17T23:14:06.043

5 Derivation of the identity $\sum_j p_j \langle \psi_j|M|\psi_j \rangle = \sum_j p_j \operatorname{tr}\left(|\psi_j \rangle \langle \psi_j|M\right)$ 2021-01-28T15:51:52.357

4 What does it mean for a result of a measurement to be known/unknown? 2018-04-23T20:07:53.377

4 'Rectilinear' and 'Diagonal' Basis in BB84 Protocol 2018-05-16T17:42:16.183

4 Measuring ancillas in Shor's algorithm 2018-06-24T18:24:06.580

4 How to calculate the off-diagonal elements of a density matrix using the measurement result? 2018-08-13T14:27:24.667

4 BB84 attack with entangled qubits example 2018-10-29T16:21:40.073

4 If a qubit is in $|1\rangle$ state, is it possible to prove that it is in $|1\rangle$ state? 2019-02-24T14:56:45.727

4 How to complete this teleportation circuit? How to create a copy of $|\psi〉$? 2019-03-18T22:19:58.870

4 Deutsch-Jozsa algorithm as a generalization of Bernstein-Vazirani 2019-05-05T00:47:41.943

4 How to determine the minimum number of experiments needed to compute m-many k-local Pauli expectations? 2019-05-30T19:45:19.607

4 Help in understanding an exercise on observable / measurement 2019-09-11T08:51:18.337

4 How to show whether two states are indistinguishable or not by measuring in a different basis? 2019-09-21T22:01:49.353

4 Physical Interpretation of Pauli Matrices as Polarization Check 2019-10-09T22:15:27.507

4 Prove that the partial trace is equivalent to measuring and discarding 2019-10-14T03:09:35.843

4 Problem with measurement error mitigation using VQE 2019-11-01T21:40:18.880

4 Are three POVM measurements on a single qubit physically realizable? 2019-11-17T00:10:18.633

4 Give an explicit example of a $d = 4$ SIC-POVM 2019-11-24T03:17:53.223

4 Quantum tomography on two qubits 2019-12-01T15:08:33.423

4 Problem with quantum tomography on two qubits 2019-12-13T14:40:36.353

4 Unentangling a qubit from a system: can we convert $\alpha|000\rangle+\beta|111\rangle$ into $\alpha|00\rangle+\beta|11\rangle$? 2020-01-25T23:08:28.613

4 Qiskit - Z expectation value from counts? 2020-04-04T22:37:04.420

4 Bra-Ket Notation and Proof of a Ket Equation in Two-Party Shared-Entanglement Setting 2020-06-27T05:34:02.783

4 How to measure the sign of quantum amplitudes 2020-07-06T16:40:07.183

4 How to measure in another basis 2020-09-05T15:47:21.003

4 What is the probability of finding the second qubit as $0$ in the state $|\psi\rangle=\frac1{\sqrt2}|00\rangle+\frac12|10\rangle-\frac12|11\rangle $? 2020-11-21T17:05:44.387

4 Computing expectation value of product of observables in PennyLane 2021-01-30T04:13:56.237

4 If the eigenvalues of $Z$ are $\pm1$, why are the computational basis states labeled with "$0$" and "$1$"? 2021-01-31T21:04:31.193

4 SWAP Test as a Projective Measurement 2021-02-09T17:13:08.353

3 Realization of Quantum Shadowgraphy 2018-06-24T16:50:17.770

3 How is measurement modelled when using the density operator? 2018-08-31T18:43:59.720

3 How to measure in an arbitrary basis in Q#? 2018-09-12T23:15:28.487

3 Calculating measurement result of quantum swap circuit 2018-10-15T23:07:18.287

3 Quantum spin measurement 2018-11-16T09:07:35.217

3 Total mutual information of a quantum system 2018-11-19T11:52:13.937

3 Convention for expressing measurement in non-standard basis 2018-11-21T20:09:54.320

3 Are projective measurement bases always orthonormal? 2018-12-03T06:58:50.657

3 Why does state preparation of 'off the shelf' qubits not follow from the Born rule (Mermin)? 2018-12-27T04:04:05.053

3 What are some examples of measuring qubits in different basis states? 2019-01-02T05:43:27.600

3 Do the probability amplitudes describe the probability of projective measurement? 2019-02-11T12:37:33.640

3 For CNOT gate with control qubit set to 1, the measured state of the second qubit unexpectedly depends on the measurement 2019-03-02T20:22:23.633

3 Why isn't the circuit performing a measurement in the Bell basis? 2019-03-03T10:11:27.533

3 How does the actual measurement collapsing an error to an orthogonal basis look like? 2019-03-13T01:24:54.743