14 Density matrices for pure states and mixed states 2018-06-14T18:55:38.513

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

8 How to check if a matrix is a valid density matrix? 2018-06-14T09:00:43.927

7 How to find a density matrix of a qubit? 2018-06-14T09:13:00.990

7 What does it mean for a density matrix to "act on a Hilbert space $\mathcal{H}"$? 2018-06-20T11:30:53.763

7 From Q# measurements to Bloch sphere 2018-06-28T09:08:57.430

7 Difference between coherence transfer, polarization transfer and population transfer? 2018-09-02T17:37:41.353

7 Is there a relation between the factorisation of the joint conditional probability distribution and Bell inequality? 2018-09-08T12:21:21.077

7 Query on Reduced Graph States 2019-11-08T08:57:35.917

7 What's the 'physical consistency' in the partial trace scenario? 2021-01-23T23:45:06.900

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

6 How do we derive the density operator of a subsystem? 2018-09-02T17:07:11.260

6 Partial trace over a product of matrices - one factor is in tensor product form 2018-12-25T08:15:27.197

6 Why do we use complex-conjugate instead of complex-conjugate-transpose when calculating the concurrence? 2019-05-24T00:58:38.740

6 Prove that $\|p^{\otimes n} - q^{\otimes n}\| \leq n \|p-q\|$ for density operators $p,q$ 2019-10-27T19:00:37.650

6 How to prepare mixed states on a quantum computer? 2020-02-13T15:28:48.693

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

6 Bob applies a projector - what happens to eigenvalues of Alice's reduced state? 2020-10-20T02:17:47.967

5 Only assuming the universe evolves according to a positive trace-preserving map, is there a proof that all subsystem evolution must be CPTP? 2018-05-17T00:23:41.620

5 Maximally mixed states for more than 1 qubit 2018-11-01T16:33:20.187

5 Is the set of classical-quantum states convex? 2018-12-27T22:13:23.120

5 Quantum teleportation with "noisy" entangled state 2019-04-17T15:16:29.680

5 How to show a density matrix is in a pure/mixed state? 2019-04-22T05:29:18.183

5 Quantum fidelity simplified formula while both of the density matrices are single qubit states 2019-06-13T16:11:03.647

5 Equivalent determinant condition for Peres-Horodecki criteria 2019-06-15T05:45:04.067

5 What's an easy way to determine a local density matrix? 2019-07-24T12:00:44.547

5 Why are $d^2$ dimensions required to describe a density matrix? 2019-12-06T15:06:15.037

5 How are the eigenvalues of $\rho=\frac12(|a\rangle\!\langle a| +|b\rangle\!\langle b|)$ derived? 2020-11-28T03:04:56.547

4 Modeling energy relaxation effects with density matrix formalism 2018-06-29T08:50:13.583

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

4 Applying CNOT with local operations and two EPR pairs 2018-10-04T21:55:14.800

4 Suggest, partly based upon limited numerical results, possible “elegant” exact formulas for Bures two-qubit separability probability 2018-10-10T21:49:55.737

4 Non-uniqueness of pure states ensemble decomposition 2019-01-24T11:40:42.563

4 Convex Combination of Separable States 2019-02-27T09:23:21.687

4 Homeomorphism or stereographic projection corresponding to the set of mixed states within the Bloch sphere 2019-03-02T23:39:45.080

4 Is there a two-qudit Choi entanglement witness $W^{(+)}$? 2019-05-01T03:56:55.710

4 Quantum state where phase information is unknown 2019-06-11T18:46:35.390

4 Understanding the classification of quantum states based on partial transposition: representations of the bipartite density matrix 2019-06-17T10:06:49.780

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

4 Proving $\langle j_2|\langle j_1| U(|0\rangle\!\langle0|\otimes\rho)U^\dagger|j_2\rangle|j_1\rangle =\operatorname{Tr}(M_j\rho)$ 2019-10-17T14:32:06.973

4 Why do purifications only differ by a local unitary? 2020-01-01T23:37:50.357

4 Applying density matrix based criterion to verify separability 2020-02-11T22:03:01.883

4 Is the quantum state fidelity defined as $F(\rho, \sigma)=\text{tr}\sqrt{\rho^{1/2}\sigma\rho^{1/2}}$ or its square? 2020-04-13T15:30:02.260

4 Semi-definite program for smooth min-entropy 2020-07-02T04:13:08.453

4 Is there a proof or example to show that a noiseless subsystem is not necessarily closed under addition? 2020-08-14T15:29:17.450

4 What is the intuition behind "states with support on orthogonal subspaces"? 2020-10-17T07:07:02.313

4 Does the quantum Jensen-Shannon divergence appear in any quantum algorithms or texts on quantum computing? 2020-11-03T11:59:55.643

4 Is the set of two-qubit absolutely separable states convex? 2020-11-11T15:09:54.403

4 How is a qubit in superposition between $|0\rangle$ and $|1\rangle$ different from a mixture of $|0\rangle$ and $|1\rangle$? 2021-01-02T00:56:22.677

4 What is the difference between $|0\rangle+|1\rangle$ and a balanced mixture of $|0\rangle$ and $|1\rangle$? 2021-02-07T23:02:03.147

4 How to express a probability distribution $P(x,y,z)= \sum_\lambda P(x|y,\lambda)P(y|\lambda,z)P(z)P(\lambda)$ in terms of a trace of a density matrix? 2021-02-16T16:17:57.617

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

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

3 What are the ranges of the four $q$ parameters in the magic simplex of Bell states formula? 2019-04-19T14:49:05.673

3 What is the average value of $|c_i\bar c_j|$ for a random state $|\psi\rangle=\sum_i c_i|i\rangle$? 2019-08-14T20:51:31.360

3 Determining the quantum secret 2019-08-27T18:50:20.103

3 How do I compute the Relative Entropy between pure and mixed states? 2019-09-27T22:00:42.467

3 Quantum Fisher information for pure states query 2019-10-16T19:05:41.247

3 What can we know about the eigenvalues of a reduced density matrix knowing the eigenvalues of the original matrix? 2019-11-02T20:44:11.460

3 What is the matrix representation for $n$-qubit gates? 2019-11-13T23:07:22.187

3 Density matrix of a product of Bell states 2019-11-26T07:32:20.220

3 What is "Lindblad Superoperator" in Stochastic Master Equation 2019-11-27T17:15:09.190

3 Simulating Classical Probabilistic Transitions with superoperators 2019-12-09T02:28:14.853

3 Find the qutrit analogue of certain qubit and ququart formulas of Li and Qiao for testing separability 2019-12-18T22:03:22.760

3 Implementation of tomography on IBM Q 2020-01-29T07:32:17.610

3 How to perform Quantum Process Tomography for three qubit gates? 2020-04-20T16:27:50.297

3 $M(\rho)=\operatorname{Tr}_2\left(\ U\ \rho\otimes\rho_2\ U^{\dagger}\right)$is unitary $\iff\ U=U_1\otimes U_2$, a product of $2$ unitary operators? 2020-05-03T16:14:37.353

3 What does it mean geometrically (in terms of vectors in the Bloch sphere) if the commutator of two density matrices $ρ_1$ and $ρ_2$ vanishes? 2020-05-20T17:53:23.390

3 Is the Hilbert-Schmidt probability simply zero that a generic rank-2 two-qubit ("pseudo-pure") density matrix is separable? 2020-07-12T18:56:36.517

3 Relation between Wigner quasi-probabability distribution and statistical second-moment 2020-07-15T18:47:33.153

3 Reduced Density Matrix Equation of Motion to describe an Ellipse 2020-08-06T15:10:48.443

3 Is the partial trace $\mathrm{Tr}_B(\rho)$ equal to $\sum_k \mathrm{Tr}[(\sigma_k\otimes I)^\dagger \rho]\sigma_k$? 2020-08-07T09:57:17.530

3 Can Alice and Bob distinguish entangled state coefficients? 2020-09-12T15:32:31.450

3 Proof of the no-communication theorem 2020-11-01T01:13:15.533

3 How can we upper bound the norm of a partial trace? 2020-11-23T21:08:01.107

3 Pure state ensembles achieving the Holevo $\chi$-quantity with at most $d^2$ states 2020-12-26T23:05:25.677

3 What's the difference between $p(i|m)$ and $p(m|i)$ in measurement? 2021-01-18T21:32:01.877

3 How do I determine if a given pure two-qubit state is separable? 2021-02-05T19:21:10.553

2 How do I construct a Density Matrix corresponding to a Hamiltonian? 2018-09-30T11:19:03.090

2 Why is a density operator defined the way it's defined? 2019-03-02T00:25:25.880

2 Purity of mixed states as a function of radial distance from origin of Bloch ball 2019-03-03T00:43:44.470

2 Decoherence in quantum systems always produces $\vert0\rangle$ 2019-03-08T01:41:32.000

2 What proportions of certain sets of PPT-two-retrit states are bound entangled or separable? 2019-04-11T12:03:52.133

2 How does the probability of measurement turn out to be negative? 2019-04-18T16:03:56.073

2 Why is the boundary of the set of states in the generalised Bloch representation comprised of singular matrices? 2019-04-29T14:37:59.510

2 What is the relevance of preservation of trace in completely postive trace preserving (CPTP) maps? 2019-05-08T07:02:54.823

2 How can I write the maximally mixed state on m qubits as a linear combination of basis vectors? 2019-06-09T14:09:39.247

2 How to represent an ensemble of pure quantum states in Qiskit? 2019-07-22T14:33:58.103

2 Trace preserving condition in Choi's thorem 2019-07-31T22:29:34.057

2 How to find the reduced density matrix of a four-qubit system? 2019-08-26T21:45:20.287

2 Trace of Hermitian Operator and Operator Function 2019-10-02T00:04:54.083

2 Does partial tracing a system with three shared Bell states give the identity? 2019-11-26T14:04:16.393

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

2 Understanding the outer products in density matrices 2020-02-21T19:32:46.210

2 What does "decoherence attenuates the density matrix" mean? 2020-02-28T21:52:36.830

2 Computation of a reduced density matrix 2020-03-12T15:44:26.803

2 Is my $|0\rangle$ state mixed or pure? 2020-05-01T21:36:46.803

2 Increasing the von Neumann entropy despite the measurement? 2020-05-04T19:47:59.510

2 Show that $I = \frac{\rho + \sigma_x\rho\sigma_x +\sigma_y\rho\sigma_y + \sigma_z\rho\sigma_z}{2}$ for all states $\rho$ 2020-05-28T00:03:26.877