All Questions
Tagged with coherent-states quantum-information
21
questions
6
votes
2
answers
639
views
When is a state entangled?
I have read from What's the difference between an entangled state, a superposed state and a cat state? that an entangled state is one that cannot be expressed as product state. Suppose we have the ...
2
votes
1
answer
70
views
How is continuous variable quantum key distribution safe against tapping some photons?
As far as I understand, CV-QKD (also here) uses coherent states to send a key, that is encoded in amplitude and phase quadratures. When someone tries to eavesdrop, this will introduce an error and ...
- 35
1
vote
1
answer
216
views
Master equation with a coherent bath
When we consider an oscillator $a$ acting with a bath of oscillators $b_i$ with the interaction Hamiltonian reads
$$H_{int}=\sum_{i}g_ia b_i^{\dagger}+g_i^*a^{\dagger}b_i,$$ with the free Hamiltonian:
...
- 442
3
votes
1
answer
310
views
What is the relationship between "quantum coherence" and "coherent states"?
What is the relationship between Quantum coherence and Coherent States?
I (almost) get the concept of Quantum Coherence when i think about it in the framework of density matrices.
I also get the ...
- 39
1
vote
2
answers
2k
views
How to derive the displacement operator from the relation $|\alpha\rangle=e^{\alpha(a^\dagger-a)}|0\rangle$?
I've been studying coherent states, an encountered a problem. My teacher told me, one can derive displacement operator via complexifying the parameter $\alpha$ in this formula:
$$|\alpha\rangle=e^{\...
2
votes
0
answers
60
views
Action of quantum channel on the state $|\alpha_x\rangle \langle \alpha_y|$
Suppose we have a coherent state with amplitude $\alpha_x$ and density matrix $\rho_x := |\alpha_x\rangle \langle \alpha_x |$. This state is sent through a quantum channel. We do not have a concrete ...
- 525
3
votes
1
answer
1k
views
Quantum Geometric Tensor and Berry Connection
The Quantum Geometric Tensor is given by
$$
\begin{split}
Q_{\mu\nu}=\langle\partial_{\mu}\psi|\partial_{\nu}\psi\rangle-\langle\partial_{\mu}\psi|\psi\rangle\langle\psi|\partial_{\nu}\psi\rangle
\end{...
- 97
1
vote
0
answers
509
views
What are the Fock-state probabilities of general Gaussian states?
A general (pure) Gaussian state has the form $\newcommand{\on}[1]{\operatorname{#1}}\newcommand{\ket}[1]{\lvert #1\rangle}\ket{\alpha,\xi}\equiv D(\alpha)S(\xi)\ket{\on{vac}}$, with $\ket{\on{vac}}$ ...
- 14.8k
8
votes
4
answers
1k
views
In what sense are spin coherent states "classical"?
Spin coherent states are often introduced as "the most classical states of a finite-dimensional system", or as the analogous of coherent states of light for finite-dimensional systems. See e....
- 14.8k
2
votes
2
answers
270
views
How to obtain the Fubini-Study metric for $SU(2)$ coherent states, using bra-ket notation?
I know that the Fubini Study metric for the $SU(2)$ coherent state is the metric on $CP^1$. The $SU(2)$ un-normalised coherent state is given by
$$
\mid z\rangle=\sum_{m=-j}^{m=+j}\sqrt{\left(
\begin{...
- 97
10
votes
4
answers
663
views
How to compute expectation value $\langle e^{iH}\rangle$ for quadratic Hamiltonians?
I have a rather basic, but actually non-trivial question:
We consider a bosonic system with creation operators $\hat{a}_i^\dagger$ and annihilation operators $\hat{a}_j$ and vacuum state $|0\rangle$ ...
- 740
2
votes
0
answers
50
views
Diagonalisation of quasi-thermal state
I have the following density operator $$\frac{1}{t \pi N} \int_{\mathbb{C}} \mathrm{d}^2\gamma \exp
\left[
-\frac{|\gamma+r\alpha|^2}{t^2 N}
\right]
|{\gamma}\rangle\langle{\gamma}|,$$
where $0\leq t,...
- 143
3
votes
1
answer
159
views
Projective measurement using two mode squeezed state?
Let me define two mode squeezed states as $ \left | \xi \right>_n=\exp\left(\xi \hat{a}^\dagger \hat{b}^\dagger-\hat{a} \hat{b} \xi^\star\right)\left | n,0 \right>$ where $\left|n,0\right>$ ...
- 67
3
votes
2
answers
360
views
Are Bi-photons and Fock States (with $N=2$) the same?
I've been researching about quantum states of light, and I came across with both terms. For what I understand of both, I think they are the same (entangled individual photons with same position and ...
1
vote
0
answers
307
views
Classical analogy for why driving a quantum harmonic oscillator creates a coherent state?
If we drive a quantum harmonic oscillator (e.g. starting from its ground state) at its resonance frequency then it will not just create an excitation in the first excited state but will create a ...
- 11