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Results tagged with quantum-mechanics
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user 165676
Quantum mechanics describes the microscopic properties of nature in a regime where classical mechanics no longer applies. It explains phenomena such as the wave-particle duality, quantization of energy, and the uncertainty principle and is generally used in single-body systems. Use the quantum-field-theory tag for the theory of many-body quantum-mechanical systems.
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Why it is necessary for a quantum map to exist that the initial state is a product state
The problem is related to the construction and the assumptions about quantum maps.
This also raises some questions about the construction itself and it has been studied extensively in the literature, …
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4
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1
answer
1k
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Physical meaning of time-varying Hamiltonian in Quantum Mechanics
I'm a self-taught in Quantum Mechanics, with the aim to understand Quantum Information theory. I have the following doubt which I cannot solve:
Assuming as a postulate that the evolution of a quantum …
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2
answers
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Prove orthonormality of displacement operators: ${\rm Tr}[D^\dagger(\alpha)D(\beta)]=\pi\del...
I'm trying to prove that displacement operators are orthonormal in quantum mechanics, e.g.:
$$\text{Tr}\{D^{\dagger}(\alpha)D(\beta)\} =\pi \delta^2(\alpha - \beta)$$
I used the completeness property …
- 440
2
votes
Decomposing a prepared quantum harmonic oscillator state
I think that a more simple solution can be obtained by noticing that your state is given by the displacement of the ground state by the factor $\mu$ [1]:
$$|\Psi_\mu\rangle=D(\mu)|0\rangle$$
where $D( …
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1
vote
Accepted
Why does E91 protocol use the CHSH inequality instead of QBER?
Quantum key distribution (QKD) algorithms can be roughly divided in two categories: prepare and measure (P&M) and entanglement-based (EB). The aim is the same: distribute information-theoretically sec …
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3
votes
Accepted
BB84 protocol vs. E91 protocol
As I explained in your previous question, both protocol are safe, as every other QKD protocol in the literature (e.g., SARG04, Decoy states, ...). The difference in the protocol is only in the practic …
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2
votes
1
answer
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Derive explicit expression of squeezed vacuum state in the Fock basis
I'm learning quantum optics, and I'm starting to manage boson algebra.
In particular, as a pure exercise, I would like to express a squeezed vacuum state in the Fock basis, which, according to Weedbr …
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0
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Homodyne detection as quantum measurement
Nice question. To be sincere, I never thought about the fact that homodyne measurement is, in some sense, an "indirect" measurement of a quadrature. Even if I 'm relatively new, I'll try to answer.
F …
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3
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CNOT and FTL communication
The reason is that the CNOT operation is not a separable operation, i.e., you cannot write $U_{NOT}=U_A\otimes U_B$ where $U_A$ acts only on the first subsystem and $U_B$ acts only on the second. In o …
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3
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Is uncertainty and correlations actualy the same thing?
Just to expand a little bit Bruce's answer...You can convince yourself about the properties of the Von Neumann entropy by proving two simple properties.
Let suppose to have a state $\rho$ in a $d$ …
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2
votes
Accepted
Does entangled states must become non entangled states after the measurement?
You must distinguish between collective measurement and separabale measurement. I think that I can answer to all of your questions starting from a simple example. Let suppose that we have a pair of qu …
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2
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Prove that in Bell's inequality $\langle{\Psi}|\left(\bf{\sigma}\cdot\bf{a}\right)\left(\bf{...
You can solve this by applying the definition of the Pauli vector, i.e.,
$${\bf{\sigma}\cdot\bf{a} }=\sigma_xa_x+\sigma_ya_y+\sigma_za_z$$
where $a_x,a_y,a_z$ are the components of $\bf a$ and $\sigma …
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