Quantum Computing Stack Exchange
Quantum Computing Stack Exchange

Most Popular

more tags
1500 questions
6
votes
2 answers

How can I show that $\mathsf{QMA}\subseteq \mathsf{PSPACE}$

Lately I have seen the claim that $\mathsf{QMA}\subseteq \mathsf{PSPACE}$, and I wonder how can it be proved. Thanks
omerna
  • 189
  • 3
6
votes
1 answer

How to show that the integral over all Haar states vanishes: $\int|\psi\rangle\,{\rm d}\psi = 0 $?

Can we show that the integral over all Haar states $|\psi \rangle $ is $$ \int |\psi \rangle \, \mathrm{d}\psi = 0~. $$ This is an integral over Haar vectors Reference to a post about what is Haar state
qc6518
  • 163
  • 2
6
votes
3 answers

Use of change of phase gates

As explained in this this answer, when we have different (relative) phases between two states, those two states will yield the same probabilities when measured in the same basis but different probabilities when measured in different bases. My…
Ntwali B.
  • 443
  • 2
  • 9
6
votes
1 answer

Is Quantum Cramer-Rao bound for single parameter always attainable?

First I will give some background of Quantum Cramer-Rao bound. There is an amount called Fisher Information:$F(\lambda)=\sum_x{p\left( x|\lambda \right) \left( \partial _{\lambda}\ln p\left( x|\lambda \right) \right) ^2}$ where $p\left( x|\lambda…
narip
  • 2,964
  • 2
  • 9
  • 32
6
votes
0 answers

Quantum State Tomography Implementation in IBMQ

I am working to understand quantum state tomography, specifically using the algorithm presented in PRL 108, 070502. This paper is referenced in IBMQ implementations of QST, both in old deprecated Ignis code (my primary reference so far) and in the…
Nathan Miller
  • 61
  • 1
6
votes
1 answer

Is it possible to extract $x_1$ and $x_2$ from $|\phi\rangle=\frac1{\sqrt2}(|x_1,0^n\rangle+|0^n,x_2\rangle)$ with non-negligible probability?

Let $\left\vert \phi\right\rangle=\frac 1{\sqrt2}\left\vert x_1,0^n\right\rangle+\frac1{\sqrt2}\left\vert 0^n,x_2\right\rangle$ be a $2n$-bit quantum state for some unknown $x_1,x_2\in\{0,1\}^n$. My question is: is it possible to extract $x_1$ and…
Henry
  • 117
  • 3
6
votes
1 answer

How could a global quantum network be realized?

This article from 2017 predicts the quantum internet by 2030. What are the biggest bottlenecks in the realization of a global quantum network (ie quantum internet)?
user820789
  • 3,302
  • 12
  • 42
6
votes
1 answer

Schmidt decomposition for tripartite system $ABC$ with vanishing mutual information between $A$ and $C$

Suppose I have a tripartite system $ABC$ in a pure state $|\psi_{ABC}\rangle$ with mutual information $I(A:C)=0$. This implies that the reduced density matrix $\rho_{AC}$ factorizes as $\rho_{AC} = \rho_A \otimes \rho_C$. How do I show that this…
nervxxx
  • 520
  • 2
  • 10
6
votes
3 answers

What physically limits qubit connectivity in superconducting chips?

All the superconducting based quantum computers I'm familiar with have a maximum of 4 nearest neighbors per qubit. Trapped ion architectures seem to be able to drive entangling gates between all pairs of qubits in devices containing up to something…
bRost03
  • 579
  • 2
  • 9
6
votes
1 answer

Why do we use the Bell state $|00\rangle+|11\rangle$ for quantum teleportation?

In the quantum teleportation protocol we use the Bell state given by $$\frac{1}{\sqrt{2}} \left( |00\rangle + |11\rangle\right). $$ My intuition tells me this works is because we can transform this Bell state to any other Bell states through a…
ljc
  • 61
  • 1
6
votes
0 answers

Is No Free Lunch Theorem generalizable to Quantum Computation?

The "No Free Lunch Theorem" says: that when averaged across all possible problems, any two strategies have equivalent performance. However it uses Bayesian reasoning to arrive at this conclusion. However, Bayesian reasoning employs conditional…
More Anonymous
  • 429
  • 3
  • 15
6
votes
1 answer

Does the Eastin-Knill theorem hold for repetition codes?

The Eastin-Knill theorem states that For any nontrivial local-error-detecting quantum code, the set of transversal, logical unitary operators is not universal. see original paper. Does this theorem hold for 1D repetition codes (e.g. a bit-flip…
Ronan
  • 163
  • 5
6
votes
3 answers

Will Moore's Law be no longer effective once quantum computers are created?

Moore's law states that computer power doubles in every 18 months (more formally: "the number of transistors in a dense integrated circuit doubles about every two years."). Statistics suggest that this observation should be correct, but aren't…
Archil Zhvania
  • 2,187
  • 1
  • 20
  • 31
6
votes
1 answer

What is the relationship between the size of the Hilbert space for boson sampling and the complexity of classical simulating it?

My intuition is that the fastest classical algorithm for simulating some kind of noiseless quantum sampling process should scale roughly with the dimension of the Hilbert space: you would need to process each amplitude at least once in order to…
tparker
  • 2,711
  • 11
  • 26
6
votes
1 answer

Quantum Ripple Carry Adder Construction

There is an excellent answer to How do I add 1+1 using a quantum computer? that shows constructions of the half and full adders. In the answer, there is a source for the QRCA. I have also looked at this presentation. I am still left with these…
user820789
  • 3,302
  • 12
  • 42
1 2 3
…
99 100