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Quantum GCD circuit: Clearing ancillae

I am currently trying to implement a circuit for computing the greatest common divisor in the Quantum Computing Language. In my work, I partially proceed from the paper Quantum Circuits for GCD ...
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23 views

Pure State Entanglement and Private Communication

My question is about the relation between two protocols of transmitting a quantum message through a Quantum channel using entanglement (entanglement Transmission or generation for this question) and ...
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0answers
19 views

Temperature influence in Optical Quantum Computing

I've recently been looking into the (perhaps a bit outdated but still very interesting) field of linear optical quantum computing. Using photons as information carriers, and using objects like ...
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0answers
14 views

Efficient ways to solve complicated kinematics problems

I'm curious about the range of approaches one can take to perform motion/kinematic simulations on many 3D objects. Currently I am familiar with the iterative process of doing such a simulation, that ...
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0answers
38 views

How does one arrive at the two qubit matrix that represents a gate? [on hold]

The two qubit CNOT gate is represented by a 2x2 matrix. However, it is also represented pictorally. How does one arrive at that matrix representation? I am not looking for "take a diagonal matrix and ...
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1answer
87 views

Quantum computing, NP complexity [closed]

Hi I have a very limited knowledge of quantum physics and its bothering me trying to understand quantum computing. I want understand how a qubit can return usable data faster then a regular bit, how ...
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0answers
75 views

Quantum computing with biological matter? [closed]

As a biologist with physics background I wonder whether there is a way to use biological matter to create quantum computers or at least to advance the field somewhat. Usually, my first feeling would ...
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0answers
42 views

How to calculate quantum cost of a reversible logic circuit?

I am trying to develop new reversible logic synthesis algorithm. But I need a good quantum cost measure for a synthesized circuit to compare my results with existing ones. For now I'm using RCViewer+ ...
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1answer
51 views

How do we imagine a Hadamard gate acting on the Bloch Sphere? [closed]

We can rewrite the Hadamard gate as $R_x(-\pi/2)R_z(-\pi/2)R_x(-\pi/2)$. I am trying to visualize the effect of applying the Hadamard gate to $|+\rangle$ on the Bloch sphere. The X gate takes ...
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1answer
36 views

Quantum circuit and Witness preserving amplification for QMA

My question is about the witness preserving amplification scheme for QMA proposed by Marriott and Watrous in 2005 (see http://arxiv.org/abs/cs/0506068 and ...
2
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1answer
279 views

Quantum algorithm for checking if element exists

I am currently having hard times while facing an interesting idea, which could speed up many present quantum algorithms, but I am not sure whether my thought is not misleading, or more precisely, ...
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1answer
40 views

Burden of proof for a quantum mechanical or classical mind [closed]

The only valid answer to the question “how does an intelligent mind work?” is currently “don’t know”. I'd like to avoid discussing how the mind could actually work as part of this question; the topic ...
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1answer
85 views

Which information is “destroyed” when a qubit is read?

A quantum bit is a unit vector in $C^2$. That is, a four dimensional unit vector. A computational basis is a pair of orthogonal vectors in $C^2$ that you choose - say, [0, 1] and [1, 0]. So the ...
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are locally unique pure quantum states also ground states of some local hamiltonian?

Let $H=\sum_i H_i$ be some k-local hamiltonian with a unique ground state $|\psi>$. Then it is easily shown that $|\psi>$ is k-locally distinguishable from any other state $|\psi'>$. Is the ...
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3answers
88 views

How much can we compute with one single qubit?

This might be a little stupid question, but I was just talking with some friends who are working in neuroscience and I tried to explain them quantum computing. When I explained them the bloch sphere ...
3
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1answer
79 views

Infinite bits to describe a qubit

In the Quantum Computation book by Nielsen and Chuang, the authors write in the context of quantum teleportation "Even if she (Alice) did know the state |w> , describing it precisely takes an ...
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1answer
58 views

Proof of inversion about the mean (Grover's) [closed]

I just have an probably trivial question, but i got stuck when deriving the inversion of the mean as used in Grover's search: I simply want to show that the application of $(2 \left| \psi ...
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1answer
55 views

Why are simulated qubits less effective?

"We could map the whole Universe — all of the information that has existed since the Big Bang — onto 300 qubits" I've seen statements like this over the years coupled with the same explanation ...
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1answer
63 views

State evolution for Dot product of quantum states (Llyod et al. 2013) [closed]

I was reading the paper by Lloyd et al. which is concerned with quantum machine learning algorithms. In the algorithm they use the evolution of the following kind (i use a reduced formula, which is ...
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1answer
38 views

Clarification on paper: “Information Flow in Entangled Quantum Systems” - David Deutsch and Patrick Hayden

Referencing paper "Information Flow in Entangled Quantum Systems" by David Deutsch and Patrick Hayden, specifically the section concerning Quantum Teleportation: ...
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0answers
23 views

Are quantum computers just massively parallel computers? [duplicate]

I am a computer engineering major so I do not understand a lot of quantum science but from what I hear about quantum computers, it sounds like they are just massively parallel computers. In quantum ...
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3answers
95 views

Are quantum computers at least build able?

Assuming a highly unrealistic where you basically have unlimited money to burn. Is it possible to a build a size scalable quantum computer? My premise is that I often read tha people have a made a ...
2
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1answer
91 views

Understanding measurement based quantum computing

I am currently reading M. A. Nielsen's review on Cluster-state Quantum Computation (Nielsen, Michael A. "Cluster-state quantum computation." Reports on Mathematical Physics 57.1 (2006): 147-161.). ...
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2answers
177 views

Nobel Prize challenge: Could neutrinos be used for quantum information processing?

We know that two scientists, Takaaki Kajita and Arthur B. McDonald, working on Neutrinos have just been awarded the 2015 Nobel Prize in Physics. My question as a Nobel Prize Challenge Question is: ...
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1answer
37 views

What determines the anyon fusion outcome (if several are possible)?

Given the fusion rule (for anyons) "A x B = 1 + C" it is possible for the anyons A and B to fuse to the vacuum "1" or to fuse to the anyon C. What determines what will happen if they fuse? Is the ...
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0answers
12 views

Is the truncated Wigner method efficiently classical simulatable?

The continuous-variable Gottesman-knill theorem says that the operation which varying the initial state described as the gaussian function (such as vacuum) to the final state described as the gaussian ...
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1answer
100 views

How can I derive Fusion-Rules for Anyons?

I am reading Pachos "Introduction to Topological Quantum Computation". Pachos writes that a model for anyons consists of a list of all anyons and a fusion rule for them. Given a model with anyonic ...
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2answers
202 views

How could memory be organized in quantum computers?

A classical computer has a memory made up of bits, where each bit represents either a one or a zero and its implemented by two-state transistor logic. However, a quantum computer maintains a sequence ...
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2answers
107 views

How Much Computing Power would be Required to Fully Simulate a Cubic Meter? [closed]

Imagine you want to simulate a cubic meter down to the particle. By following the Standard Model and other basic physical equations, how much computing power would be required to do this, in say, a ...
2
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1answer
74 views

Eigenvalues of density operator under quantum channel

Consider a 2x2 density operator $\rho$ with eigenvalues $\lambda_{1},\lambda_{2}$ (where $\lambda_{1}\geq\lambda_{2}$) evolving into a 4x4 density operator $\rho'$ (with eigenvalues ...
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1answer
272 views

Quantum and classical scaling of memory

In the literature of Quantum Computation (QC), when discussing the simulation of quantum systems, one usually comes across comparisons with the classical digital analog such as: "Classically the size ...
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2answers
59 views

Rotation Operators [closed]

How can I rotate a state $|\psi>=\alpha|0>+\beta|1>$ to $|\psi'>=\delta|0>+\gamma|1>$ using a unitary U, where the values of $\alpha, \beta, \gamma, \delta$ are known?
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2answers
44 views

Is this model of a finite quantum coprocessor violating physical principles?

I want to consider a classical computer without any artificial restrictions, which has a single quantum coprocessor with a fixed finite number of qubits. It can perform the following three types of ...
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1answer
67 views

Relationship between Toffoli gate and Deutsch gate

I am reading a book called "Quantum Computing for computer scientists" and stuck at this exercise for a day. Bellow is the description of Deutsch gate: And here is the description of Toffoli ...
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2answers
113 views

Quantum computers for string theory? [closed]

I read something about that locating our space in the multitude of multidimensional spaces of M-theory (and so identifying particular particles which we can measure with particular strings) is a too ...
2
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1answer
345 views

Controlled Phase Gates

The Quantum Fourier Transform consists of 2 gates. Controlled Phase Gates, and Hadamard gates. I'm assuming the Controlled Phase Gate is a combination of a Control Gate, and a Phase Gate. But what ...
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How is this circuit equivalent to a Bell measurement?

The circuit elements are : CNOT gate, first qubit is the control bit Hadamard gate (H) The dials represent measurements made in the computational basis Therefore, the circuit (without the ...
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0answers
34 views

How to find a single coefficient of quantum Fourier transform reliably

Quantum Fourier transform transform $X \in \mathbb{C}^{2^n}$ to $Y \in \mathbb{C}^{2^n}$. Suppose one wishes to find $y_0$, the first coefficient of "vector" $Y$. However, as this is quantum process, ...
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1answer
62 views

Can a classical 50/50 probability be distinguished from a quantum superposition with a single measurement?

$\renewcommand{\ket}[1]{|#1\rangle}$ A "false" (equally superimposed qubit) is created by mechanically firing with 50/50 probability a resonance photon at a Hydrogen atom qubit in the ground state. ...
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1answer
65 views

Is a universal quantum computer expected to be able to shed any light on the measurement problem? - Part B [closed]

Following up on Part A. Suppose we build a universal quantum computer and it functions as we currently expect it to. Is there any reason to suggest that, beyond its uses for things like ...
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0answers
79 views

Is a universal quantum computer expected to be able to shed any light on the measurement problem? - Part A [closed]

Suppose we build a universal quantum computer and it functions as we currently expect it to. Is there any reason to suggest that, beyond its uses for things like cryptography and quantum system ...
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1answer
140 views

How is classical information put into and retrieved from a quantum computer?

How, if you had to find the factors of say a 256 digit number, would you go about inputting the data and how do the proper answers "drop out" of a quantum computer. Other than terms such as qubits, ...
0
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1answer
71 views

Classical Computation without NOT [closed]

Is it possible to do universal classical computation using bits and 2-bit gates when you cannot perform a NOT operation on a single bit (hence cant do CNOT and so on). If yes, what are the possible ...
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7answers
6k views

Could quantum computers break any cipher? [closed]

I've been told that physicists and computer scientists are working on computers that could use quantum physics to increase significantly computation capabilities and break any cipher so cryptography ...
0
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1answer
83 views

What are typical error rates of quantum computers?

I read in an article that in order to perform error correction on a quantum computer there can only be one error per 10.000 calculations (=unitary transformations). This sounds pretty high but how ...
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1answer
52 views

Why does a measurement on one qubit force another one into a given state in Simon's algorithm?

This comes from trying to understand the "Simon's algorithm". So we have a set of $2^n$ kets $|x_i >$ one each for $i \in \{0,1\}^n$. Each $x_j \in \{0,1\}^n$. And we have the further constraint ...
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3answers
97 views

The $n$-th root of the NOT gate

I simply can not find material containing facts about the $n$-th root of the NOT gate and it's realization in Q.M. and also in C.M.. Does anyone have material? A comparison of the $n$-th root NOT ...
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1answer
65 views

What causes continuous errors in a qubit?

I read that due to decoherence a qubit in a superpositon gets destroyed or put into one definite eigenstate. This kind of error seems to occur due to interactions with other stuff like the environment ...
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1answer
77 views

Quantum computing can be done via measurement alone, why is this significant?

I read in the Afterword section of Nielsen and Chuang's book Quantum Computation and Quantum Information that A second area of progress has been in understanding of what physical resources are ...
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1answer
137 views

Approximating a target operator

I was wondering if anyone knew how the author got to equation 12 on page four of this paper, I will attempt to explain the situation below. Given $C$, a target operator, we wish to create an ...