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.
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At what time exactly does decoherence happen? and retrodating
Take a qubit initialized to $|0\rangle$. Apply a Hadamard transform to it. Measure it with an apparatus along the $|0\rangle,\, |1\rangle$ basis. If zero, spare a living cat. If 1, kill the cat. ...
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177 views
What is the difference between quantum cryptography and quantum teleportation?
Generate two entangled photons, send one to a message sender and the other to the intended receiver. Both the sender and the receiver recover the same piece of quantum information from the photons, ...
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106 views
How to deterministically distinguish the following quantum states?
(1) How to deterministically distinguish the following quantum states:
$$\frac{1}{\sqrt{2}}[|+0\rangle|0\rangle+|-1\rangle|1\rangle$$,
$$\frac{1}{\sqrt{2}}|-0\rangle|0\rangle+|+1\rangle|1\rangle$$,
...
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142 views
Quantum Coin Flipping Protocol
$\newcommand{\ket}[1]{\left|#1\right>}$
I have the next protocol:
$A$ tosses a fair coin $a\in \{0,1\}$, if $a=0$, $A$ sends to $B$ $\ket{\psi_0}=\ket0$, if $a=1$ $A$ sends to $B$, ...
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2answers
169 views
fermions and quantum gates
say that i have 2 qubits - 2 spin half fermions.
my initial condition is |00> in the spin-wave function and some anti-symmetrical spacial wave function.
I'm wondering about what happens when applying ...
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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 ...
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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} | ...
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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} ...
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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, ...
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109 views
Entanglement and conservation
Is the following assertion sufficiently unique to merit a paper? Every absolute conservation law implies a corresponding form of entanglement, not just spin (angular momentum). Linear momentum ...
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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.
...
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1answer
58 views
Landauer's principle vs Wien's displacement 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 argue ...
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1answer
51 views
Qubit initial state
Suppose that a qubit in an initial state that we don't know was measured, and the result was 1.
Is it possible to know the initial state of the qubit by the result measured? And if the result would ...
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1answer
141 views
Quantum communication
Is it possible to get two atoms to opposite quantum states of one another so when I change the state of first one, the state of the other one changes too? Is it possible to move them to another place ...
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1answer
141 views
Two Qubit problem
A two-qubit system was originally in the state $ \frac{3}{4}|00\rangle-\frac{\sqrt{5}}{4}|01\rangle+\frac{1}{4}|10\rangle-\frac{1}{4}|11\rangle $ , and then we measured the first qubit to ...
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1answer
32 views
Violation of the Normalization Constraint?
Say we have two qubits $|a\rangle$ and $|b\rangle$ both initialized to $|0\rangle$. We then apply the rotation gate $R_{x}(\frac{\pi}{2})$ of matrix representation
$\left( \begin{array}{}
...
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1answer
64 views
Question on hadamard gate and cnot gate circuit tables
I'm trying to solve this problem for homework:
Now show that if the CNOT gate is applied in the Hadamard basis - i.e. apply the Hadamard gate to
the inputs and outputs of the CNOT gate - then ...
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1answer
67 views
Information bearing degrees of freedom of a quantum simple harmonic oscillator
I am trying to make sense of arXiv:physics/0210005. I am confused with the concept of information bearing degrees of freedom of a system mentioned at the very beginning. To verify the arguments of the ...
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1answer
166 views
Quantum circuit, two control not gates
Consider the quantum circuit in the picture below:
We have a Hadamard gate followed by a CNOT gate, this puts the 2nd & 3rd state in the bell state $\beta_{00}=\frac{1}{\sqrt2}(\mid 00\rangle ...
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1answer
101 views
Latest advances in experimental quantum processors?
I'm and undergraduate student and I'm doing a report on Quantum computing. As a conclusion of my report I'd like to highlight the latest experimental advances in Quantum Computing, especially in ...
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1answer
119 views
Using Quantum Teleportation in a way to have the effect of matter teleportation
So, I understand that quantum teleportation is the transfer of a quantum state from one particle or system of particles and its correlations to another receiving system consisting of particle(s). ...
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1answer
52 views
Building some measurement appratus that distinguish between two mixtures
We have a measurement $M$ that distinguishs between $\rho_1$ and $\rho_0$, if it has three possible answers 1,2,3 and whenever it answers something different than 3 it's correct.
$M$ succeeds with ...
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38 views
Deutsch-Jozsa algorithm [closed]
How many calls are required to determine is the function balanced or not on the classical computer with probability of error < 50%.
Ref: Deutsch-Jozsa algorithm.
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1answer
60 views
Two qubits problem [closed]
Given the 2 qubit state:
(a/b) |00> + (c/b) |01> + (c/b) |10> + (d/b) |11>
What is the probability that 2 qubits are equal?
Thanks much!
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45 views
Constructing a Toffoli gate from CNOT and single-qubit gates [closed]
Toffoli gate in terms of CNOT and single-qubit gates.
Thanks much!
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2answers
70 views
Purpose of Grover's algorithm?
How is the output of Grover's algorithm useful if the result is required to use the oracle? If we already know the desired state, what's the point of using the algorithm?
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56 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} ...
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27 views
Circuit identities HTH [closed]
Using this circuit indetities $HXH=Z, HYH=-Y, HZH = X$ prove $HTH=R_x(\pi/4)$. here $H$ is Hadamard matrix, $X,Y$ and $Z$ are Pauli matrix, $R_x$ is a rotation matrix and $T=\left[ \begin{array}{cc}
1 ...
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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. ...
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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 ...
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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 ...
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0answers
64 views
Quantum circuit simulation software [closed]
Would anyone be able to recommend some software that you can use to simulate a quantum circuit? Something someone created to easily be able to create nice looking quantum circuits and quickly ...
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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, ...
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211 views
Computing with qubits [closed]
We have a qubit in the state $|\psi \rangle= √3/2 |0\rangle + 1/2 |1\rangle$, which we want to measure in the $cos \theta\ |\theta\rangle + sin \theta |1\rangle, sin \theta |\theta\rangle - cos θ ...
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16 views
OAM states in communications [duplicate]
Possible Duplicate:
OAM states for wireless communications
Can someone give me an overview of how OAM states are used in communications?
Using Orbital Angular Momentum States seems like a ...
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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 ...
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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 ...
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144 views
Quantum Compting or DNA computing [closed]
My friend and me are working on DNA computing and on some improvements to it.
Of course, we are working on computing aspects of this branch. So, we have insufficient knowledge about physics and ...
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19 views
Is the universe a quantum computer - is light speed barrier a computational constraint [duplicate]
Possible Duplicate:
Is the universe a quantum computer - is light speed barrier a computational constraint
Cross-posting this question, since physics.stackexchange has not provided any ...
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2answers
99 views
Quantum gate: Phase shift
I dont undestand how to apply a phase shift gate to a qubit. By example how to map $|\psi_0\rangle = \cos (30^\circ) |0\rangle + \sin (30^\circ) |1\rangle$ to $|\psi_1\rangle = \cos(-15^\circ) ...
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1answer
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How is a Rydberg Blockade Radius defined?
Rydberg blockade is a phenomena in 3 or more level systems of Rydberg dressed atoms.
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1answer
76 views
Quantum gates Hadamard before a toffoli gate
After applying a Hadamard gate so that the state splits into either $|1\rangle+|0\rangle$ or $|0\rangle-|1\rangle$ what happens when applying a ccnot (toffoli) gate, this flips a third qbit if the ...
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1answer
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2 following gates, inverse circuit
I have a circuit that has 4 wires and 2 following each other Toffoli gates.
The first Toffoli gate occupies 3 wires from above, the following Toffoli gate occupies 3 wires from below.
What will look ...
