Quantum information is the study of the informational content of quantum states. The most common object of study is the "qubit", the information in a two-state quantum system such as spin-1/2 or photon polarization.

learn more… | top users | synonyms (1)

2
votes
2answers
73 views

Entanglement in single particle state

Is it possible that we have entanglement in different degrees of freedom of a singe particle. like spin and linear momentum .
0
votes
2answers
169 views

Can you read and write a quantum state to a particle without collapsing its probability field?

I know the main problem with a quantum computer is that you can't read and write data from it until after it has run though all of its calculations. But would reading and writing quantum data to ...
0
votes
2answers
84 views

Calculating states of entangled and disentangled qubits

I'm writing a quantum computer simulator (about 8 qubits) and I know most of the basics (i.e. how to calculate the effect of a quantum gate on a qubit). But I have hit a wall. Is it possible, with ...
8
votes
1answer
112 views

Does quantum collapse involve a loss of information? Does it require energy as suggested by the Landauer Limit?

I read in the context of quantum computing or of the minimal energy required for computation that there has to be a minimum possible amount of energy required to change one bit of information, called ...
5
votes
1answer
97 views

Is there a handwavy way to explain what quantum correlation means?

Is there a simple way to explain the difference between a classical and truly quantum correlation to a non-quantum person who has basic understanding classical correlation? I mean without invoking ...
3
votes
1answer
108 views

Trying to understand mixed states

I took a basic quantum chemistry course (McQuarrie's "Quantum Chemistry"), but it never dealt with mixed states -- only pure states (or if it did, we never got to it in class). So I'm trying to ...
2
votes
1answer
75 views

Quantum Fourier Transform and Entropy

QFT is a nonlocal unitary transformation and so can generate entanglement in a system. It means a separable pure state can be converted into an entangled pure state. Now since the presence of ...
2
votes
1answer
31 views

Deriving Rabi rotation matrix

I want to understand where the matrix: $$ \left|\psi(t)\right> = \binom{a(t)}{b(t)} = \begin{bmatrix} cos(\Omega t/2)&-ie^{i\phi_L t}sin(\Omega t/2) \\ -ie^{-i\phi_L t}sin(\Omega t/2) & ...
2
votes
1answer
33 views

What are the practical consequences of “approximate” quantum cloning with a stimulated emission cloning machine?

Say I build some stimulated emission-based cloning machine for photons (e.g. some active laser medium). Alternatively I could do cloning via interference, e.g. a linearly polarized photon could be ...
2
votes
1answer
84 views

Quantum fluctuations in a classical domain?

"In the presence of chaos, even small fluctuations (including quantum fluctuations) can be amplified to produce large uncertainties in later behavior"(http://arxiv.org/pdf/gr-qc/9210010v2.pdf) Is there ...
2
votes
1answer
43 views

How to write a noisy state as a separable operator

Bipartite operators close enough to the identity are separable. But how does one compute the product operator terms of the separable expansion? In particular, if $\left| \Phi \right> = m^{-1/2} ...
1
vote
1answer
53 views

How many states are there in the observable universe

If we took a single instant and considered all possible states of all energy and matter do we have any bounds on how much that would be? Would that number be related to information?
0
votes
1answer
33 views

Why is this entangled?

I am studying a book of quantum computing and the author gives an example of a four qubits separable! He writes: Let $\left|ψ\right> = \frac 1 2(\left|00\right> + \left|11\right> + ...
0
votes
1answer
46 views

Does all information in the universe come from the observer?

In absence of the observer any system undergoes unitary evolution, that is reversible evolution without entropy change. It is believed that the initial state of the universe had very low entropy, ...
0
votes
1answer
38 views

Significance of 'chiral' form for a quibit?

Say I have a qubit with probability amplitude divided evenly among $|0>$ and $|1>$ $$\frac{1}{\sqrt 2}|0> + \frac{1}{\sqrt 2}|1>$$ So it seems that we have a, loosely speaking, ...
0
votes
1answer
61 views

Design a quantum circuit from a matrix

I have unitary matrix and I would find the quantum circuit associated. There are 3 qubits input so it's a 8x8 matrix but it's not a simple operation. The number of gates is not specified. Is there a ...
-1
votes
1answer
34 views

Classical Information carrying capacity of two states

What classical information is carried by $\alpha|0\rangle+\beta|1\rangle$ and $\alpha|00\rangle+\beta|11\rangle$? How to quantify it? To be specific, A GHZ state, $\frac{1}{\sqrt ...
1
vote
0answers
45 views

Adiabatic evolution for initial Hamiltonian on Hadamard basis and problem Hamiltonian as diagonal

This is spawned from a comment at the answer to one of my previous questions. Someone suggested to me that claiming the following statement might be NP-hard. Could anyone please help me to figure out ...
1
vote
0answers
81 views

Is there a known generalization of the Schmidt decomposition based on a maximal set of “locally recorded branches”?

I came across an unusual multi-partite generalization of the Schmidt decomposition in my work, which I describe below. Usually, when people say "a multi-partite Schmidt decomposition", they mean a ...
1
vote
0answers
98 views

What is the energy scale of a Hamiltonian?

On the second page of this paper a term 'fundamental energy scale' is used while talking about a Hamiltonian. The context is implementing Deutsch's algorithm using Adiabatic Quantum Computation. What ...
1
vote
0answers
73 views

How large must the Quantum teleportation fidelity have to be in order for it to be useful?

This question relates and stems from my original question. Please read this one and the comments before answering this question. Quantum Teleportation Fidelity I know that for discrete variables ...
1
vote
0answers
52 views

Finding all marked element by Grover search(not in superposition)

Quantum search enables square-sped up search for marked element. When there are multiple maked element, grover search provides only superposition of them. If I want to find all the marked elements, ...
1
vote
0answers
66 views

Equivalence of simple formulations of qubit entanglement

I'm reading some very elementary treatments of quantum computation and am unsure about the correspondence among "definitions" of qubit entanglement. One definition states that (1) the bits of a ...
1
vote
0answers
65 views

Experimental realization of Quantum Teleportation of Spin, not polarization, not ions or atoms

I've looked everywhere in databases my school provides, to google searches, to the questions asked in physics forums, and here. As I understand, the original QT (quantum teleportation) protocol ...
1
vote
0answers
71 views

Matrix separability preservation under conjugation?

Someone know any paper about matrix separability preservation under conjugation? A well know result is that Clifford group preserve the Pauli group under conjugation or, in other words: $C(P_{1} ...
1
vote
0answers
244 views

Could one transmit a signal with equally-tuned casimir plates across the quantum field?

It seems, one could exploit the Casimir effect to send messages across arbitrarily-large distances with carefully-tuned Casimir plates. Obviously, relativity would preclude FTL information transfer, ...
0
votes
0answers
26 views

Proving two forms of atom-field interaction perturbation Hamiltonian are equivalent

In the presence of an electromagnetic field in the dipole-approximation (${\boldsymbol A} = {\boldsymbol A}(0,t)$) we have the two forms $$H_{{\boldsymbol d}\cdot {\boldsymbol E}} = - q {\boldsymbol ...
0
votes
0answers
24 views

Bragg's diffraction and Simon's problem

In Preskill's notes, John Preskill goes as If we scatter a photon off of a periodic array of needles , the photon is likely to be scattered in one of a set of preferred directions , where the ...
0
votes
0answers
17 views

Where does the requirement of prime number dimension figure in generating mutually unbiased bases (MUB)?

I have been studying this paper by S. Bandyopadhyay et al. - "A new proof for the existence of mutually unbiased bases". Here is the link. They explicitly construct MUB using generalized Pauli ...
0
votes
0answers
19 views

relationship between Fredkin gate and the swap and I gates

I need to prove this relationship: $$G_{Fredkin} = I \otimes |0\rangle\langle 0| + G_{swap} \otimes |1\rangle\langle 1|$$ with $$G_{swap} = |00\rangle\langle 00| + |01\rangle\langle 10| + ...
0
votes
0answers
43 views

range of the difference of two-qubit density matrix determinants

The determinant of a two-qubit (4 x 4) density matrix lies between 0 and (1/2)^8. (A pure state has determinant zero, and the fully mixed [classical] state, determinant (1/2)^8.) The determinant of ...
0
votes
0answers
49 views

kadanoff and cohomology

for those that combine Homology group and some form of Kadanoff scheme for coarse graining on a lattice, am I having a good argument when saying this: (practical thinking now) 1. I obtain the Homology ...
0
votes
0answers
49 views

Can quantum entanglement increase in the semiclassical limit?

In the paper Classical Dynamics of Quantum Entanglement. Giulio Casati, Italo Guarneri & Jose Reslen. Phys. Rev. E 85 no. 3, 036208 (2012); arXiv:1109.0907, the authors state that the ...
0
votes
0answers
13 views

How many how many planck areas would capture of a resting electron add to the surface of a black hole?

In other words, what is the 'information content' of an electron (or of other supposedly elementary particles for that matter) as revealed by their effects on black hole horizon area?
0
votes
0answers
55 views

Double-slit experiment formulated in a quantum circuit

What would the double-slit experiment or something analogous to it look like implemented as a quantum circuit/program? Also, what about the delayed choice quantum eraser, how would that look in a ...
0
votes
0answers
39 views

How can a qubit superposition state be written to a quantum register?

If a 3 qubit register can simultaneously store all 8 possible values in superposition, then how it is achieved to write 8 values in to the register? And How these 8 values can be processed parallel to ...
0
votes
0answers
161 views

Continous and Discrete basis, Multiplication of Density Matrix and Hamiltonian

Suppose I have a wave function $\psi(x)$ in position basis. I can make a density function by simply multiplying $\psi(x)$ and its conjugate $\psi^*(x)$. If I operate the density matrix ...
0
votes
0answers
35 views

Finding all marked elements using Grover's algorithm

As part of an assignment I am supposed to design a variant of Grover's algorithm that finds all $t$ marked elements. I guess like most people I'm more familiar with classic computation, so the ...
0
votes
0answers
81 views

How to measure the arbitrariness of a quantum state?

An arbitrary qubit is represented as $\alpha|0\rangle+\beta|1\rangle$ with $|\alpha|^2+|\beta|^2=1$. If we know either $\alpha$ or $\beta$, the state can be completely identified. The 'arbitrariness' ...
0
votes
0answers
76 views

Hamiltonian matrix propertu

A professor made an statement to prove the variational theorem: Because the Hamiltonian (H operator of quantum physics) is diagonal in its own eigenfunction, the terms in $\left \langle \Phi _{m} ...
0
votes
0answers
79 views

Landauer's principle vs Rayleigh–Jeans law

Can we argue based on Landauer's principle that if one bit information is changed inside a blackbody, the total radiated energy should be at least or in order of $kTln2$? If it is so, can we also ...