All Questions

1
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1answer
16 views

Module BasicAer not found

After installing qiskit-terra via git (pip install qiskit), all python programs involving the line ...
2
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0answers
10 views

Solution enumeration algorithm?

Suppose I have a quantum algorithm that produces, as solutions more than one different linear combinations with raised probability amplitudes. Each solution is correct in the context of this ...
2
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0answers
12 views

What does teleportation have to do w/ XOR linked lists?

I am trying to wrap my head around the correlation between repeating teleportation & XOR linked lists. I understand that: "the quantum equivalent of the one time pad (i.e. XORing a message with ...
3
votes
0answers
22 views

Clock matrix vs matrix clock

In the process of research leading up to my previous question, I found out about matrix, vector & logical clocks. The citation in the aforementioned question mentions clock and shift matrices. ...
3
votes
1answer
19 views

Generalizing quantum teleportation for qudits

In an answer to a previous question, Generalization for n quantum teleportations, Craig Gidney states: The more complicated way to generalize teleportation is figuring out how to make it work on ...
1
vote
1answer
30 views

Multiple random coin flips without measurements

The question is similar to this one. As suggested in the answer, I can easily do this with just one qubit: I repeatedly Hadamard it and measure in order to have a fair coin flip at every point. The ...
2
votes
1answer
26 views

Partial Trace over a complicated looking state

In the Quantum Operations section in Nielsen and Chuang, (page 358 in the 2002 edition), they have the following equation: $$\varepsilon(\rho) = tr_{env} [U(\rho \otimes \rho_{env})U^\dagger]$$ They ...
1
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1answer
59 views

Depolarizing channel operator sum representation

In Nielsen and Chuang, it is shown that the operator sum representation of a depolarizing channel $\mathcal{E}(\rho) = \frac{pI}{2} + (1-p)\rho$ is easily seen by substituting the identity matrix with ...
2
votes
1answer
92 views

Are there emulators for quantum networks?

Inspired by the question Are there emulators for quantum computers?, I'm curious to know if it's possible to emulate a quantum network on a classic computer. Additionally, is it possible to emulate a ...
3
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2answers
51 views

Shannon entropy is least when Measurement basis = Mixture basis

For a one qubit system, take a basis. Call this the mixture basis. Consider only basis states and classical mixtures of these basis states. Definition of Shannon Entropy used here: Defined with ...
3
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0answers
45 views

How do I build a gate from a matrix on Qiskit?

I'm creating a gate for a project and need to test if it has the same results as the original circuit in a simulator, how do I build this gate on Qiskit? It's a 3 qubit gate, 8x8 matrix: $$ \frac{1}{...
2
votes
1answer
51 views

Why can't you run a teleportation circuit on an IBM Q device?

I'm studying teleportation circuits with this tutorial and just out of curiosity, why can't a teleportation circuit be run on an IBM Q device?
2
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1answer
49 views

Print circuit compiled on hardware?

I would like to see the compiled circuit as executed on a hardware. Nominally, this sequence of commands should return the QASM circuit in the variable ran_qc, but ...
4
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2answers
73 views

Grover's algorithm with W-state

In the general form of Grover's algorithm, we start with the uniform superposition of n qubits. Now, suppose instead that we start with a generic state, for example ...
3
votes
2answers
54 views

How to fix? 'E1101:Instance of 'QuantumCircuit' has no 'h' member' and 'E1101:Instance of 'QuantumCircuit' has no 'cx' member'

I'm using this simple code to test my Qiskit and learn how to use it but it keeps giving this problems, how do I fix it (Using VS Code and Anaconda Python 3.7) ...
2
votes
1answer
36 views

Understanding why the modular function part of Shor's algorithm is unitary

I've been struggling to understand the modular exponent bit of Shor's algorithm. My understanding is that it takes a register in the state $\frac{1}{\sqrt{Q}}\sum_{k=1}^{Q-1} |k\rangle |0\rangle$ to ...
1
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2answers
553 views

Measuring but not looking at the result

Once a state is measured, but we don't look at the result, is the state now written as a density matrix, that is, the probability that it could land on a measurement operator multiplied by the ...
2
votes
1answer
38 views

How to formulate the master equation for three systems?

I have a three composite system of the form $H_{\text{tot}}=H_{ab}\otimes H_c$ where the system $C$ is behaving as the dissipator or the environment (I can model it as a thermal bath). And it is ...
1
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1answer
50 views

Building a matrix corresponding to the teleportation circuit

I'm trying to build the matrix that corresponds to this quantum teleportation circuit, but it never works when I test it in the quirk simulator, I tried finding the matrix corresponding to every part ...
1
vote
1answer
37 views

Proof of no-cloning

I was reading a proof of No-cloning theorem, there are a couple of steps that are not clear to me, but the book does not give explanation for them. So here it is: Theorem: It is impossible to create ...
4
votes
1answer
47 views

Expected repetitions of the quantum part of Shor's algorithm

Shor's algorithm to factor a number $N$ goes as follows: Pick a random value $b \in (0, N)$. Use a specific quantum computation to a sample a value $v$ that should be close to $2^{m} k/p$ where $m$ ...
8
votes
1answer
139 views

Isomorphism between the Clifford group and the quaternions

How do I find an explicit isomorphism between the elements of the Clifford group and some 24 quaternions? The easy part: The multiplication of matrices should correspond to multiplication of ...
5
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1answer
181 views

Problem with the mathematical formulation of “qubitization”

In this research paper, the authors introduce a new algorithm to perform Hamiltonian simulation. The beginning of their abstract is Given a Hermitian operator $\hat{H} = \langle G\vert \hat{U} \...
2
votes
1answer
60 views

qiskit - Is there any way to discard the results of a measurement?

I have a circuit composed by n qubits, plus a single one which is an ancilla. I'm making multiple measurements on the ancilla at different stages of the circuit, ...
1
vote
1answer
49 views

Multiple random coin flips

Suppose that in my circuit I have to generate multiple, say n, random coin flips. For example, this coin flips could be used to activate ...
5
votes
1answer
43 views

Proof on approximating adiabatic evolution by quantum circuit

I am reading on how the adiabatic evolution can be approximated by a quantum circuit of size poly(nT) and I am trying to follow the derivation in the paper W. van Dam, M. Mosca, and U. Vazirani, “...
2
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0answers
20 views

Speedup Prange ISD using Grover

In his 2009 paper, Grover vs McElicee, Bernstein proposed to use the Grover's algorithm to obtain a quadratic speedup on the Prange ISD. However, it is not quite clear to me in which part of the ...
2
votes
1answer
206 views

Is it possible to expand/merge different circuits?

Suppose I have created a circuit composed of some registers with the usual qc = QuantumCircuit(qr, cr) where qr and ...
2
votes
1answer
36 views

CNOT gate - control qubit is in superposition

If a control qubit is in superposition, how it will affect target qubit if it is collapsed or in superposition? Is it true that CNOT works only if the control bit collapsed to 1? Also, is it possible ...
3
votes
2answers
64 views

Time-bin encoding qudits

Time-bin encoding is a technique used in Quantum information science to encode a qubit of information on a photon. Wikipedia Is there a generalization for $n$-th level qudits?
2
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0answers
117 views

Eigenvalues of CPT operator

Suppose we define an operator CPT that carries out the CPT transformation: $$\text{CPT}|\Psi\rangle = A|\Psi\rangle$$ where A is just a constant. Or put another way, the states of our theory are ...
3
votes
1answer
35 views

How many Kraus operators are required to characterise a channel with different start and end dimensions?

If we have a quantum channel mapping from a $d$-dimensional state to a $d$-dimensional state, it can be described by at most $d^2$ Kraus operators. Suppose our channel maps instead from a $d_1$-...
4
votes
2answers
69 views

How to get all combinations of given input?

I'm stuck with a very specific problem that I'm not sure on how to implement using quantum gates. Suppose I have an n qubit circuit and that I want in output a ...
2
votes
1answer
41 views

Measuring order ancilla qubits in surface code

Recently I have been reading about surface codes a little and one thing I came acros was a specific order in which gates should be applied before the ancilla is measured. See for instance figure 2 in ...
2
votes
1answer
42 views

Why are these circuits not producing the same output?

I am simulating the phase shift algorithm on the Quirk platform. Even when the endian-ness of the built-in inverse QFT gate is corrected for, the circuits still output different results. Shouldn't the ...
7
votes
0answers
90 views

Quantum algorithms for problems outside NP

What is known about quatum algorithms for problems outside NP (eg NEXP-complete problems), both theoretically like upper & lower speedup bounds and various (im)possibility results, as well as ...
4
votes
1answer
46 views

Implementation of inverse QFT?

When implementing the inverse quantum Fourier transform, in addition to reversing the circuit, does one need to take the conjugate transpose of the phase shift gates in the circuit as well?
3
votes
1answer
31 views

How are nonlocal games used in device-independent quantum cryptography?

As I understand it, device-independent quantum cryptography enables you to safely perform cryptographic operations without necessarily trusting the quantum device on which they are performed. Nonlocal ...
2
votes
1answer
38 views

Why are these circuits not producing the expected output?

This circuit was created on the Quirk platform. I'm trying to implement a basic case of phase estimation. For some reason, I'm getting this strange result. When the Inverse QFT is broken down, it ...
2
votes
2answers
85 views

Non-layperson explanation of why a qubit is more useful than a bit?

I have a computer science and mathematics degree and am trying to wrap my head around quantum computing and it just doesn't seem to make sense from the very beginning. I think the problem is the ...
1
vote
2answers
61 views

A question about notation for quantum states

I am reading an article on representation of digital images using qubits. But I am not able to understand the notations of the article. Can somebody help me: $|0\rangle$: It means the first basis ...
3
votes
1answer
28 views

Are the order finding and period finding algorithms the same thing?

Do they both just use similar methods of calculation, or are they completely interchangeable?
1
vote
1answer
30 views

Do these outputs seem normal for the order finding algorithm?

I'm sorry for posting so many questions about this specific problem, but I just want to make sure that I am implementing an algorithm correctly. I am simulating the order finding algorithm (finding ...
2
votes
1answer
31 views

Is this the correct quantum circuit for the order-finding algorithm?

The algorithm is being implemented on Cirq, with the goal of finding the smallest $r$ for cooprime numbers $x$ and $N$ satisfying the equation $x^r \ = \ 1($mod $N)$. I have set $x \ = \ 2$ and $N \ = ...
2
votes
0answers
31 views

Dephasing channels

I'm taking a quantum information course and one of my exercises says to find $p,p'$, for which there is a channel $\tilde\Lambda(\Lambda(\rho))=\Lambda'(\rho)$, where $\Lambda$ and $\Lambda'$ are ...
4
votes
1answer
71 views

Construction of ${R_n(\theta)}$ using only the Hadamard and ${\pi/8}$ gates

In the "Quantum Computation and Quantum Information 10th Anniversary textbook by Nielsen & Chuang", they claim that Eqn(4.75) is a rotation about the axis along the direction ( ${cos(\pi/8)}$, ${...
3
votes
1answer
31 views

What's the notion of input size for Quantum Verification?

I've been looking into $\mathsf{QPIP}_\tau$ as a complexity class. The following will be a summary of definition 3.12 in Classical Verification of Quantum Computations by Urmila Mahadev. A language ...
6
votes
1answer
95 views

Why is this implementation of the order finding algorithm not working?

I asked a question about this earlier, but I am still coming across problems in my algorithm implementation. I am trying to implement the order finding algorithm on Cirq finding the minimal positive $...
0
votes
2answers
85 views

How to prepare a superposed states of odd integers from $1$ to $\sqrt{N}$?

$\newcommand{\q}[2]{\langle #1 | #2 \rangle} \newcommand{\qr}[1]{|#1\rangle} \newcommand{\ql}[1]{\langle #1|} \newcommand{\floor}[1]{\left\lfloor #1 \right\rfloor} \newcommand{\round}[1]{\left\lfloor #...
3
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2answers
188 views

Are projective measurement bases always orthonormal?

Are projective measurement bases always orthonormal?

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