Questions tagged [quantum-algorithms]

For questions about quantum algorithms, that is, sequences of quantum gates, operations, and measurements, whose purpose which achieve some goal. Standard examples are Shor's and Grover's algorithms.

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Can quantum algorithm still success if some gates fail and cannot be measured?

I know the power of quantum computation is to simultaneously compute all the qubits if they are entangled. I wonder if the quantum algorithm is still functional if one of the quantum gates fails (...
Amanli's user avatar
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Problem with SwitchCase in qiskit while using general unitary gate

I am trying to run a circuit using SwithCase Op on one of the 127 qubits backends. My code is the following: ...
Navid Elyasi's user avatar
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Difference between PQCs and VQCs

I'm going through this TensorFlow tutorial on quantum machine learning. The code implements reinforcement learning algorithms based on parameterized/variational quantum circuits (PQCs or VQCs). What ...
Medulla Oblongata's user avatar
2 votes
1 answer
108 views

Is there an "in place" Toffoli gate?

I am trying to implement the multiplication of a scalar in $\mathbb{Z}_2$ and a polynomial in $GF(2^n)$ in Qiskit. One naive method of implementation that I can think of is: ...
Ash Ketchum's user avatar
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1 answer
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Need help regarding building a custom VQE

I want to write code for a custom Variational Quantum Eigensolver (VQE) capable of computing eigenvalue(s) for non-Hermitian systems, based on this paper. I have formulated a cost function (provided ...
Bravyi's user avatar
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How is controlled constant addition implemented for binary polynomials?

So, currently I am going through the paper Concrete Quantum Cryptanalysis of Binary Elliptic Curves. The section on point addition mentions that for adding two points $P_1$ and $P_2$, they assume that ...
Ash Ketchum's user avatar
2 votes
1 answer
250 views

Why does the definition of the oracle in Deutsch's algorithm fail to specify its action on superpositions?

I’m trying to understand the Deutsch algorithm. I can see that the math shows the algorithm to be correct, but I don’t understand how the math represents the given conditions. The oracle is supposed ...
Jon Vote's user avatar
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Open Source Quantum Algorithm Development projects

Is there a platform where people contribute together to solving tasks in the area of quantum algorithm development?
Lazloo Xp's user avatar
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How write a marking oracle if greater than with Q#?

I'm trying to write a code to find a minimum in a list. I follow this paper : A quantum algorithm for finding the minimum. So I need to write an operator to mark the case $T [j] < T[y]$. My idea is ...
Cyrano's user avatar
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Why is "reducing Hamiltonian energy" also optimizing a Quantum Machine Learning model?

From what I observed, most hybrid qml architectures surround the ideas of Hamiltonian states, and it seems like our goal to optimize a circuit is to keep energy states as low as possible. But why is ...
Ryan Wang's user avatar
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quantum algorithm for multilevel/hierarchical dataset

The Radon dataset is a well-known hierarchical/multilevel dataset. It contains Radon samples from houses in counties across the United States. The goal of the model is to estimate the (log) Radon ...
inq's user avatar
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Confusion about simulation of projective measurements

The authors present an algorithm to obtain a state that is proportional to the solution of a system of linear equations. The algorithm works by evolving with a hamiltonian $H(s+ \delta)$ on the ground ...
Bruno's user avatar
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What is the intuition behind uniform Hadamard superposition?

I noticed that in many quantum algorithms, you apply a layer of uniform Hadamard transformation before and after the operations in between. For example, Deutsch-Josza, Simon's, and Grover's search. ...
Ryan Wang's user avatar
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Preparation of Grover’s algorithm: How to implement the oracle $U_f$?

In order to understand Grover’s algorithm, we need to be able to implement $U_f$ from a black box implementing $f$, which we know how to do. Suppose you have this black box as we can find in some ...
NotaChoice's user avatar
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Does qiskit make any rounding errors or anything similar, or is it a perfect (but slow) simulation of a quantum computer?

I ran the following circuit to calculate the real part of the Bargmann Invariant of a system of quantum states. The invariant is defined as ...
Srini Thirumalai's user avatar
1 vote
1 answer
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qiskit statevector ordering issue

I am currently studying Qiskit. I don't understand the two pictures below while studying. When I apply circuit.x(1), the X gate should be applied to the second qubit, resulting in the state |01>. ...
junghyunHa's user avatar
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Imaginary bases lead to complex entropy. Is complex entropy useful in quantum computing? [closed]

I'm working through the Programming Drill 10.2.1 from Quantum Computing for Computer Scientists. I am not a student; this is not homework. I'm just doing this for my own betterment. I notice that ...
shawn_halayka's user avatar
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Product for block-encoding of two density operators

I know for density operator like $\rho$, we have a block-encoding matrix with purification operator and SWAP gate: $BE_{\rho} = \begin{bmatrix} \rho & \cdot \\ \cdot & \cdot \end{bmatrix}$. ...
Dan David's user avatar
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Self referencing algorithms for multiplication of binary polynomials

Currently, I am going through the paper "Space-efficient quantum multiplication of polynomials for binary finite fields with sub-quadratic Toffoli gate count" by Iggy van Hoof. Two ...
Ash Ketchum's user avatar
1 vote
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How can I initialize a classic register in qiskit?

is there a way to initialize a classic register in qiskit? I will go quickly through my problem and then suggest one solution but I am not satisfied with that and ask if there is another solution. ...
Qubii's user avatar
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Implementing a Quantum Recurrent Neural Network

I want to implement a Quantum Recurrent Neural Network and use it for time series forecasting. As a starting point, I chose to implement it using the architecture given in this paper: https://arxiv....
MoBlufiz's user avatar
2 votes
1 answer
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What is the difference between shot and iteration of the quantum circuit?

Hi this question is stem from What is meant with "shot" in quantum computation?. If we just look for the distribution of the result, is there any theoretical difference between method 1 and ...
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Problem with the mathematical definition of the eigenvalue algorithm on a specific exercise

I think I understand well how the eigenvalue algorithm works but when I try to define it mathematically I have problems. Specifically I have the matrix U: $$ U = \begin{pmatrix} 0 & i \\ i & 0 ...
Francescov20's user avatar
2 votes
1 answer
159 views

Problem with eigenvalue evaluation algorithm application on matrix $U$

Once I get to the end of the algorithm, I can't understand how to calculate the eigenvalue using formulas. Bear in mind that it is an exercise to be carried out with pen and paper. the matrix of $U$ ...
Francescov20's user avatar
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Are there quantum algorithms to estimate the partial transpose?

The entanglement negativity and the positive partial-transpose criteria play important roles in quantifying the amount of entanglement for mixed states. Yet, because these measures generally involve ...
ironmanaudi's user avatar
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1 answer
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How much complexity is required to implement $\text{C$_\Pi$NOT}$ gate?

The projector-controlled not gate $\text{C$_\Pi$NOT}$ is defined as $$\text{C$_\Pi$NOT} \, \colon= \Pi \otimes X + (\mathbb{I}-\Pi)\otimes\mathbb{I}\,, \tag{1}$$ in András Gilyén et. al. (2018)[arXiv:...
Takimoto.R's user avatar
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Outputing classification probability from the Qiskit VQC

I am new to Qiskit. For the last few days, I have been trying to train my first VQC to do some classification task. Now the VQC is successfully running but it could only output a label whenever I ask ...
Zhelun Li's user avatar
1 vote
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67 views

Can Amplitude Amplification amplify an unknown state? [duplicate]

If you have for example the basis states $|000\rangle$ and $|xxx\rangle$. The value of the second basis state is unknown, but the amplitude of both states is given. Also the amplitude of the second ...
Manuel's user avatar
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Quantum improvement in collision-free ID assignment problem?

Consider the following: you are a network device that is in charge of assigning unique identifiers (consisting of $b$ bits) to new devices as they join the network. However, you do not have very much ...
Franklin Pezzuti Dyer's user avatar
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Can adiabatic quantum computing be used to find local minimum instead of ground states?

We know that with unfriendly energy gap circumstances, adiabatic quantum computing takes exponential time to find a ground state of some hamiltonian. But if some local minimum state is all we look for,...
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How do I apply Amplitude Amplification for following state?

I have a multi qubit state that consists of two basis states and looks like the following for different number of qubits: 2 qubits: $|00⟩+|xx⟩$ 3 qubits: $|000⟩+|xxx⟩$ 4 qubits: $|0000⟩+|xxxx⟩$ ... (...
Manuel's user avatar
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1 vote
1 answer
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How is a linear combination of pauli operators applied to a quantum circuit in qiskit?

Consider a quantum circuit of 2 qubit: quantumcircuit = QuantumCircuit(2) If one wishes to apply a Pauli-X operator to the first qubit, one writes: ...
Physkid's user avatar
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4 votes
1 answer
284 views

How to measure in $\sigma_x$ basis in Qiskit? [duplicate]

As we know, Qiskit can give us the results of our measurements in computational or, better to say, $\sigma_z$ basis. However, I am courageous about measuring the qubit in, for instance, $\sigma_x$ ...
Navid Elyasi's user avatar
4 votes
0 answers
46 views

Quantum volume calculation: what is the significance of the value 2/3 for probability to observe a heavy output in the definition of achievable depth?

I am looking into the algorithm to calculate the quantum volume of a given quantum computer. The one thing that is unclear to me is how the achievable depth is defined. In Andrew W. Cross, Lev S. ...
QVolume's user avatar
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5 votes
2 answers
174 views

Why is it hard to prove complexity bounds for variational algorithms?

I'm not very familiar with variational algorithms, but I've heard people say that they're "heuristic" and it's difficult to measure their performance via complexity analysis. Why is this the ...
confusion's user avatar
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1 vote
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ZNE for mitigating errors in probability distribution results

Can ZNE be applied to mitigate errors for getting the probability distribution in the computational basis rather than mitigating errors for calculation of expectation values?
Amey Meher's user avatar
4 votes
1 answer
98 views

Retrieving job result attributes in Qiskit

I am trying to optimize a Hamiltonian using QAOA in IBM Qiskit. I used the following 'minimize' function to get my result. (I am not including the whole code because it will get unnecessarily long). <...
Jane's user avatar
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2 votes
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What's a quantum algorithm in the black box model to find $j_1,j_2$ such that $f(x_1,...,x_n)=x_{j1}\oplus x_{j2}$?

Consider the set of all functions $f : \{0, 1\}^n → \{0, 1\}$ that are of the form $f(x_1, x_2, . . . , x_n) = x_{j1}\oplus x_{j2}$ for some distinct $j_1, j_2 \in \{1, 2, . . . , n\}$. Suppose that ...
metaUser's user avatar
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0 answers
38 views

How can one use QAOA to obtain parameters that approximate the first excited state of the target Hamiltonian?

One can use QAOA to find the ground state and its energy by minimizing the expectation value of a target Hamiltonian (say, $H_T$) with respect to the QAOA ansatz and obtaining optimal parameters ...
Pratham Hullamballi's user avatar
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how to measure $Tr[M\rho_1N\rho_2]$ on NISQ devices?

To evaluate $Tr[M\rho]$ with $M$ and $\rho$ a tensor product of Pauli operators and a density matrix, respectively, we just need to prepare the state $\rho$ and then measure it in the $M$-eigenbasis. ...
刘环宇's user avatar
1 vote
0 answers
24 views

How to implement the graph adjacency array model?

The paper "Quantum query complexity of some graph problems" by Durr et al. introduces the adjacency array model as a way of storing a graph on a quantum computer. For a vertex $v_i$ of ...
mmmmmmmnm's user avatar
1 vote
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65 views

Quantum Lookup Table circuit

I am trying to use the paper "A Realizable GAS-based Quantum Algorithm for Traveling Salesman Problem (2022)". However, it never explains how the index converter works, beyond it being a ...
MrStealYourFrog's user avatar
2 votes
1 answer
90 views

Does the quantum state fidelity satisfy $F(\rho ,\sigma) \le F(\mathcal{A}(\rho), \mathcal{A}(\sigma))$ if ${\cal A}$ is a process involving ancillae?

It is a well known fact that the fidelity is preserved by unitary evolution, i.e. $$ F(\rho ,\sigma) = F(U\rho U^\dagger, U\sigma U^\dagger), $$ for any unitary operator $U$. However in most quantum ...
SRichoux's user avatar
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3 votes
0 answers
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Intuition for failure of strong Fourier sampling for the symmetric group

I am trying to read and understand the following two papers: The Symmetric Group Defies Strong Fourier Sampling: Part I The Symmetric Group Defies Strong Fourier Sampling: Part II I have a pretty good ...
Jackson Walters's user avatar
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62 views

Is it possible to simulate a quantum algorithm on a classical computer? [duplicate]

I am designing a quantum algorithm that I would like to simulate and test, but I need to be able to simulate it on a classical computer.
Mihir Macwan's user avatar
1 vote
2 answers
99 views

A Decision Algorithm That Maybe Related to Quantum Search

As is well known Grover's algorithm can invert a function on a domain of 2^n possible values in other words it can find an x such that f(x)=1 if such an x exists for the oracle f(x). Suppose we are ...
Chez's user avatar
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2 votes
2 answers
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gate actions in classical (not in the physics sense) superdense coding narrative

I am currently reading through superdense coding and the setup is as follows: Both Alice and Bob shares a fixed entangled state $|\psi\rangle = \frac{1}{\sqrt{2}}[|00\rangle + |11\rangle]$ with the ...
Physkid's user avatar
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2 votes
2 answers
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Is there a quantum algorithm for this?

While a well-established quantum algorithm exists for finding an estimate of the phase of the eigenvalue of a unitary matrix, the following question has a bit of a different requirement. Suppose we ...
Chez's user avatar
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5 votes
2 answers
722 views

What is a Hadamard test?

What is a Hadamard test? I have seen this term at many places in video lectures and on various weblinks. A detailed answer on this would be a great help. This is what Wikipedia says, but I really ...
Manu's user avatar
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1 vote
0 answers
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Comparing BQM and CQM solving for a tree-path problem

I'm currently working on a project for my thesis regarding BQM and CQM optimisation for a path problem. Without going too much on the details, here's some info: the structure is a tree, where all the ...
Amedeo Bertuzzi's user avatar

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