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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Arrow of Time in Information transfer

I am writing a sci-fi script and need some legitimate theory to back up a central story element (so there's no real world application): Could there be a logically consistent theory supporting the ...
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What does it mean that quantum teleportation can be classically simulated?

Quoting here from Quantum Computation by Neilsen and Chuang : (Gottesman–Knill theorem) Suppose a quantum computation is performed which involves only the following elements: state preparations ...
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Is it sensible to speak of the parity operator in 4 dimensional Hilbert space?

So I'm dealing with a system of two qubits, with the hamiltonian given by $$H = \left[ \begin{array}{cccc} a & 0 & -b & 0 \\ 0 & 0 & 0 & -b\\ -b & 0 & 0 & 0\\ 0 ...
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Entanglement Distillation - Interpretate a protocol

I have a general question to the interpretation of a enganglement distillation protocol. In general you have a set of entanglet qubit pairs in a Werner-state. Point of matter of this is that I can ...
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What is a good book for quantum mechanics and quantum computation? [duplicate]

I am looking for a book in quantum computers for self-learning.The kind of book that teaches quantum-mechanics + quantum-computation. I have basic understanding in calculus , linear-algebra (like ...
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Dicke states, spin squeezing and quantum metrology

Dicke states are by definition simultaneous eigenstates of the $J_z$ and $J^2$ operator. What is the difference between these states and Dicke squeezed (DS) states? I know that these are "entangled" ...
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Question about Hartle and Hawking's universal wavefunction?

My apologies in advance if this question is poorly worded or doesn't make any sense, however I have just finished reading into this theory and it seems as though Hawkings No Boundary Universe is ...
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Quantum chaos in interacting discrete time quantum walk?

I have situation where I am simulating discrete time quantum walk (DTQW) for various graphs. I have two quantum walkers on the graph and they can interact with each other by the fact that where the ...
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Why can't classical information be transmitted through quantum entanglement by measuring time between change events? [duplicate]

If the effect of measurement in quantum entanglement occurs instantaneously why can't it be used to transmit classical information faster than light? I'm based my question off this seemingly well ...
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Why consciousness should not be a reason for quantum decoherence?

As postulated by Stuart Hameroff in his article "quantum consciousness",that it is one of the reasons for reduction of quantum superposition. Roger Penrose suggested that consciousness is not ...
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What is the most general definition of a bosonic Gaussian state?

I am reading this paper where the definition of the bosonic state is mentioned on page 2 here :- http://arxiv.org/pdf/0806.1625.pdf . From a general definition of any density operator in terms of ...
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Projection of Quantum State onto Bell State

I am very interested by this paper on entanglement swapping and timelike entanglement. The one thing I get really tripped up with is the whole idea of a projection onto a bell basis. I understand ...
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Ising formulation of the graph isomorphism problem

Context I have been going through Ising formulations of many NP problems by Andrew Lucas. In section 9 on page 22, the author gave an Ising formulation of the graph isomorphism problem. Here I ...
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preparing qutrit mixed state

I have a problem: Ok so I want to create a superposition qutrit state, like this: $$ |\Psi\rangle=\frac{1}{\sqrt{3}}(|0\rangle+|1\rangle+|-1\rangle) $$ is it possible to go there, starting with an ...
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I would like to ask any interested reader about “Quantum Bidding in Bridge”

see http://journals.aps.org/prx/pdf/10.1103/PhysRevX.4.021047 I would like to see how specific examples are worked out. Specifically, details on how the quantum protocol in figure 1. of the above ...
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Quantum Bit Commitment, restricting ourselves to pure states

I have been going through the Preskill lecture notes on quantum computation, and there is a question on Quantum Bit Commitment: Alice wants to make a prediction, either $0$ or $1$, before an ...
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120 views

Quantum Simulation of Schrodinger's equation

While studying some quantum mechanics from Neilsen's book on quantum computing and came across following because x and p are conjugate variables related by a quantum Fourier transform: $ ...
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Density matrix as a simple state

I computed eigenvalues and eigenvectors of a density matrix for state $a|0\rangle+b|1\rangle$. For eigenvalue $0$ for example, I obtain an eigenvector $(-b^*/a^*, 1)$ before normalization. Now I would ...
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Exhaustive list of assumptions for the Clauser-Horne-Shimony-Holt inequality

I am trying to create an exhaustive list of all assumptions which work as the base of the CHSH inequality. Locality - this means an object can be influenced only by its surroundings. So, the events ...
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Projection operators and their subspaces (of Hilbert space)

I've been watching Susskind's lectures on Quantum Entanglement, and something he said regarding (non-)commuting projection operators confused me. Consider two subspaces {$|a>$} and {$|b>$} of ...
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Significance of 'chiral' form for a quibit?

Say I have a qubit with probability amplitude divided evenly among $|0\rangle$ and $|1\rangle$ $$\frac{1}{\sqrt 2}|0\rangle + \frac{1}{\sqrt 2}|1\rangle$$ So it seems that we have a, loosely ...
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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 ...
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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 ...
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Information carried by single photon

In Quantum Information we can use photons for quantum bits (qubits). What i often read is that each photon can carry one unit of information, i.e. using the polarization state of a single photon. I ...
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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| + ...
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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 ...
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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 ...
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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 ...
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52 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 ...
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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?
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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 ...
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132 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 ...
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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 ...
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How does a vacancy become mobile during annealing?

The Nitrogen Vacancy (NV) centre is a defect in diamond consisting of a substitutional nitrogen atom accompanied by a vacant nearest-neighbour lattice site. Substitutional nitrogen impurities are ...
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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 ...
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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' ...
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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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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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How to construct this oracle quantum gate?

I was reading the paper Quantum Computational Complexity in the Presence of Closed Timelike Curves. In this the author mentions that following quantum oracle gate which operates on $n+1$ qubits, can ...
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342 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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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, ...
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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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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 ...
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Studying Physics [closed]

I'm preparing for entry into a Physics degree course, and was planning on a double major in Physics (with a specialization in Quantum Information later) but am now considering a minor in ...
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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 ...
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Why do we believe in a “force” driven universe? [closed]

Why do we not believe in the potential for a "unified force field" universe, to the exclusion of the belief in the potential for a mechanical, gear driven universe, if the correct shape for the gear ...