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.
5
votes
2answers
99 views
Toric Code and Random Bond Ising Model
It was established by Dennis, Kitaev et al. that the 2D Toric Code
can be mapped to a 2D Random Bond Ising Model. The original derivation
was given in the paper "Topological quantum memory" which ...
2
votes
2answers
58 views
Is it possible to use quantum mechanics for an effective time based encryption?
This is for an application in cryptography. There is a concept called "time based cryptography", where a message can be decrypted only after a certain time, Say "12/12/2060, 12:30 GMT". There are some ...
8
votes
1answer
73 views
Many body quantum states analyzed as probabilistic sequences
Measurements of consecutive sites in a many body qudit system (e.q. a spin chain) can be interpreted as generating a probabilistic sequence of numbers $X_1 X_2 X_3 \ldots$, where $X_i\in ...
6
votes
1answer
177 views
Entangled or unentangled?
I got a little puzzled when thinking about two entangled fermions.
Say that we have a Hilbert space in which we have two fermionic orbitals $a$ and $b$. Then the Hilbert space $H$'s dimension is just ...
3
votes
1answer
146 views
Why are the equal probabilities for Bell state measurement outcomes essential for “quantum teleportation”?
I've recently been introduced to the basics of finite-dimensional quantum mechanics from a purely mathematical point of view (with a quantum-information theme to it). When discussing quantum ...
3
votes
1answer
395 views
Size of a quantum computer to effectively calculate macroscopic reality from quantum mechanics
Assuming the correctness of QM: Would the size of such a computer be smaller than the observable universe? If it were to represent all available information in the universe it seems that it's minimal ...
2
votes
1answer
23 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
40 views
Statistical sum of physical quantities in a quantum system
Let $C = A + B$ (statistical sum, so $\mathbb{E}[C] = \mathbb{E}[A] + \mathbb{E}[B]$), and let $p(A = a) = 1$. Are the following true?
$\mathbb{E}[C^2] = a^2 + 2a\mathbb{E}[B] + \mathbb{E}[B^2]$
...
12
votes
0answers
212 views
Bell polytopes with nontrivial symmetries
Take $N$ parties, each of which receives an input $s_i \in {1, \dots, m_i}$ and produces an output $r_i \in {1, \dots, v_i}$, possibly in a nondeterministic manner. We are interested in joint ...
7
votes
0answers
110 views
What is a Hilbert space filter?
In a recent paper,
Side-Channel-Free Quantum Key Distribution, by Samuel L. Braunstein and Stefano Pirandola. Phys. Rev. Lett. 108, 130502 (2012). doi:10.1103/PhysRevLett.108.130502, ...
4
votes
0answers
67 views
Shape of the state space under different tensor products
I am currently studying generalized probabilistic theories. Let me roughly recall how such a theory looks like (you can skip this and go to "My question" if you are familiar with this).
Recall: In a ...
3
votes
0answers
112 views
projective measurement & POVM
Let us consider the following completely positive map $\mathcal{B}(\mathbb{C}^n)\ni\rho\mapsto L\rho L^\dagger$, where $L\in\mathcal{B}(\mathbb{C}^n)$ is any arbitrary operator (and can have rank ...
3
votes
0answers
84 views
POVM advantage in state discrimination
Suppose we are given the task of discriminating, with minimum error, between a set of states $\{|\psi_1\rangle,|\psi_2\rangle,\ldots,|\psi_N\rangle\}$. In other words, we are given an unknown state ...
3
votes
0answers
71 views
Concurrence in higher dimensions?
Does anybody know of any calculation of the concurrence for some mixed state other than the qubit-qubit case (which was solved by Wootters)?
3
votes
0answers
69 views
are pinch-off bubbles valid solutions to general relativity?
are bubbles of spacetime pinching-off allowed solutions to general relativity? With "pinch-off bubble" i really mean a finite 3D volume of space whose 2D boundary decreases until it reaches zero and ...
3
votes
0answers
65 views
Known properties of a specific class of quantum states
Recently, I have been studying a quantum protocol for the "Hidden Matching" problem that makes use of states that can be expressed as
$|\psi\rangle=\frac{1}{\sqrt{n}}\sum_{i=1}^n ...
2
votes
0answers
69 views
decoherence free subspace of a single photon
Take the state vector for a single photon as
$\psi = \int \gamma_{\omega} | \omega \rangle \otimes (\alpha |H \rangle + \beta | V \rangle )d \omega$
$H, V, \omega$ are the horizontal polarization, ...
2
votes
0answers
97 views
Separable states of maximum non-classical correlations
Although there is no standard measure of entanglement, the GHZ states
$|GHZ\rangle=\frac{1}{\sqrt{2}}(|0\rangle^{\otimes n}+|1\rangle^{\otimes n})$
are often deemed as maximally entangled states of ...
2
votes
0answers
53 views
Are there any connections between James–Stein estimator and quantum mechanics?
Very nice statement from wiki:
When three or more unrelated parameters are measured, their total MSE can be reduced by using a combined estimator such as the James–Stein estimator; whereas when ...
1
vote
0answers
54 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
53 views
fiber optic second order PMD as an operator on the tensor product Hilbert space
Second order polarization mode dispersion (SOPMD) is a coupling mechanism between polarization and frequency. Take our photon to be the following tensor product:
$\psi = \int \gamma_{\omega} | ...
1
vote
0answers
61 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
200 views
Could someone 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, ...
1
vote
0answers
46 views
Looking for description of Helstrom's measurement
I hope someone can help me find the page or chapter where Helstrom discusses his famous measurement for distinguishing between two mixtures in the textbook Quantum Detection and Estimation Theory.
...
0
votes
0answers
38 views
Creating matrix Hamiltonian for Feynman's CNOT
I'm trying to read Quantum Mechanical Computer and to implement the CNOT logical gate with some analytical software.
Since i wish to use the SWITCH implementation of the CNOT [Fig.8] i've realized ...
0
votes
0answers
54 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
43 views
Partial Measure Probability
Let be a
$$|\psi\rangle = \dfrac{3}{5\sqrt{2}}|00 \rangle- \dfrac{3i}{5\sqrt{2}}|01 \rangle+ \dfrac{2\sqrt{2}}{5}|10 \rangle - \dfrac{2\sqrt{2} i}{5}|11 \rangle$$
state with two qubits. ...
0
votes
0answers
35 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 ...
0
votes
0answers
45 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 ...
0
votes
0answers
22 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, ...
0
votes
0answers
55 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 ...
0
votes
0answers
109 views
State of the entangled particles at the event horizon of black hole
Looking through the article of Samir Mathur http://arxiv.org/abs/0909.1038
he assumes that the entangled particles created at the event horizon have all the state ...
