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Questions tagged [algorithm]

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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Some of the qubits are not evaluated at Qiskit

When I implement a 3-qubit circuit in Qiskit, circuit is executed smoothly at the simulator but counts I read back as results does not contain all of the qubits that are defined and included in the ...
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3 votes
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27 views

How is this Variational Quantum Singular Value Decomposition paper efficient in any way?

Link to paper here. This algorithm seems neat but the unitary decomposition of the matrix M generally takes an exponential number of Pauli basis elements in the number of qubits $N$, therefore an ...
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Grover search with index register entangled with ancilla

I have a question: when Grover's search is set up with ancilla qubits in an entangled state, does it still work or not? Consider an example with a 4-size search space. Firstly, we use 2 qubits ...
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Why does Qsample encoding require N Qubits for encoding size N probability distribution?

I'm reading Supervised Learning with Quantum Computers book https://link.springer.com/book/10.1007/978-3-319-96424-9. In the data encoding section, Qsample encoding is one of the techniques to encode ...
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2 votes
1 answer
31 views

Iterative quantum phase estimation - real device

I'm trying to implement the iterative quantum phase estimation on a real (IBM) quantum computer. I'm using the code below. When I run this code on a simulator the results are the expected ones, but ...
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1 vote
1 answer
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I have question about cost of 'modular multiplication unitary' in Shor's algorithm

Here modular multiplication unitary means $U_a : |s\rangle \to|as\mod N\rangle$. My main question is, can the modular multiplication unitary $U_a$ can be constructed in time polynomial in the number ...
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1 vote
0 answers
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The enery levals crossover problem in Quantum Annealing

How to avoid energy levals crossover in quantum annealing by Kibble-Zurek mechanism? Any detailed references?
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2 votes
1 answer
36 views

Convexity of cost function in quantum machine learning

I have a small confusion on convexity of the most typical cost function considered in many qml papers: $\text{Tr}(\rho O)$, where $O$ is a Hermitian operator and $\rho$ is a quantum state. This is ...
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2 votes
1 answer
136 views

Is there a quantum algorithm to find the xor of a dataset

Given a black box function f taking an input of length n bits, is there a quantum algorithm which can find the xor of all possible outputs of f, in less than 2^n calls to f?
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1 vote
0 answers
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Slight issue with QFTing two qubits

Let's consider two qubits and the corresponding computational basis $\{|0\rangle\, |1\rangle, |2\rangle, |3\rangle\}$. In binary form, any of these vectors can also be written as a product $|x_1\...
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3 votes
2 answers
62 views

Understanding the output of a Deutsch-Jozsa circuit

I'm looking at the Deustch-Jozsa algorithm. While reading this Qiskit tutorial. I didn't understand what the presented result in plot mean. That is, why the output 1111 means a balanced function? What ...
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5 votes
1 answer
746 views

Is 60% accuracy high when calculating 1+1 on a quantum computer?

A financial firm has criticized the quantum computer of a company called IonQ. Part of the content is that IonQ's quantum computer is only 60% accurate for 1+1 calculations, and only 50% for 2+3 ...
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What are the main approaches allowing to efficiently simulate quantum circuits, and which hypotheses those circuits have to fulfill

In general, it is very computationally intensive to simulate the evolution of a quantum system. However, in some particular cases, an efficient classical simulation of a quantum algorithm is possible. ...
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1 vote
1 answer
28 views

From Hamiltonian to the Pulse Sequence

I know my Hamiltonian: I know which unitary I want to have. Suppose that I want to have this matrix from Hamiltonian: How can I find the pulse sequence to have this matrix from the Hamiltonian? What ...
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2 votes
1 answer
93 views

Applicability of the Bernstein-Vazirani to different modulus

The Bernstein Vazirani can solve s for f(x) = s(dot product) x mod 2. My question is if its possible to modify this to work for mod 3,4 etc. Is this even possible? Edit: Whats the probability of the ...
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2 votes
1 answer
88 views

Exponential advantage with Hadamard test

My question is the following: Let's assume that the only algorithm a quantum computer would be able to implement is the Hadamard test, which circuit is represented below, would we say that compared to ...
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1 vote
1 answer
67 views

Can the Bernstein-Vazirani algorithm be applied to a remote classical function?

Can the Bernstein-Vazirani algorithm be applied to a remote classical function? As in, a function we are not able to set up an oracle for and is completely classical?
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Generating a random 16-digits in a superposition state using Qiskit

Im trying to create a script using Qiskit for a days but somehow i couldn't seem to get it done!! Im new to QuantumComputing, so pardon me if i don't explain something properly. I need to create a ...
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2 votes
1 answer
554 views

How does a quantum computer find the correct password faster than classical computers using brute-force?

I didn't get this part right! For example, we have an online box with a 16-digit password, and we don't know what the password is! How can a quantum computer find the correct password faster than ...
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2 votes
0 answers
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How to obtain an expression of the complexity of the period-finding algorithm with respect to the period length?

Intro. Nielsen and Chuang in Quantum computation and quantum information on section 5.4.1 state that the period-finding algorithm has a runtime of $U + O(L^2)$ operations where $L$ is the size of the ...
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3 votes
0 answers
80 views

Solving Wordle using quantum computing

I have read everything available on how to solve Wordle using many different strategies ( classical approaches ) However, I wonder if Wordle can be approach using Quantum computing to solve the ...
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4 votes
1 answer
116 views

Is it essential to apply Quantum Singular Value transformation twice for Hamiltonian simulation?

I have been reading the paper A Grand Unification of Quantum Algorithms and I need clarification on the Hamiltonian simulation algorithm provided in the paper on page 23. . In procedure part point 2 ...
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1 vote
1 answer
336 views

Why is the combination of NTRU Prime and X25519 ECDH in OpenSSH believed to be secure against quantum attacks?

What do you think about the combination of NTRU Prime and X25519 ECDH in OpenSSH 9.0? Why is the combination of NTRU Prime and X25519 ECDH in OpenSSH believed to be secure against quantum attacks in ...
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0 votes
0 answers
30 views

Can quantum computer handle large time complexity algorithm? Or how large can it? [duplicate]

For an algorithm with time complexity O(2^n^n^n^n^n^n^n^n), we do not wish to implement it in classical computers because of its growth. Is it the same for quantum computers? How large can it handle ...
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2 votes
2 answers
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Estimating imaginary part of an inner product of two quantum states

Suppose I want to estimate $Im(\langle \psi_1\lvert \sigma_x\lvert \psi_2\rangle)$ by using quantum circuit. At first, I thought of using the Swap test, but since it gives $|\langle \psi_1|\psi_2\...
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2 votes
0 answers
25 views

Why is lattice-based cryptography believed to be hard to solve for quantum computers?

Lattice-based cryptography is said to be the main contender for a post-quantum cryptography framework. It's thought that instead of having to switch everything over to QKD, post-quantum algorithms can ...
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9 votes
1 answer
2k views

Can a quantum computer break quantum cryptography?

I’m not sure if this makes sense, but I know that there is quantum and post-quantum encryption, and I’m curious whether quantum computing can break a quantum encryption.
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Is there a toy oracle to show the feasibility of Grover's algorithm?

Is there any small 'toy' oracle that can show the feasibility of Grover's algorithm for searching (without using the geometric rotation interpretation)? It is confusing that we cannot know the ...
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6 votes
2 answers
181 views

Proven quantum advantage (in the algorithmic sense) without error correction (for specific algo, or noise models)

I would like to know if there are some specific class of quantum algorithms, under some hypotheses about the noise model behind the quantum gates for which we know that there is an exponential ...
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5 votes
2 answers
832 views

Are there quantum algorithms showing a double exponential advantage?

I would like to know if there are known quantum algorithms that provide a double exponential advantage compared to the best known classical algorithms. More precisely, if the characteristics of the ...
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0 votes
1 answer
55 views

What is the definition of $n$-local commuting circuit?

In this paper and this one, they talk about commuting quantum circuits that are only composed of "$n$-local commuting circuits", typically for $n=2$ or $n=3$. However they don't provide a ...
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2 votes
1 answer
65 views

Can the oracle in the Deutsch-Jozsa algorithm be neither balanced nor constant?

I know that the oracle $U_f$ has to be either constant or balanced. But what if $f$ is an AND function? I know in that case it is neither. So my question is what happens if $U_f$ is neither constant ...
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3 votes
1 answer
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Quantum Fourier Transform on $\mathbb{Z}_R^n$

I am reading Regev's proof of existence of quantum algorithm to sample from a discrete Gaussian distribution given a CVP oracle and I am confused about his calculation of the Quantum Fourier transform ...
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3 votes
2 answers
103 views

Tapering off qubits

Suppose you have a Hamiltonian of the form $$ H = ZXXX + YXXX + XXXX $$ where $Z,X,Y$ are the usual Pauli matrices with $ZXXX = Z \otimes X \otimes X \otimes X$ and similar for the other two terms. ...
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5 votes
1 answer
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Review on quantum resources required in mixed-state quantum computing

I am trying to see which features we know are necessary for mixed-state quantum computing to avoid the algorithms being efficiently simulated on classical computers. In the case of pure-state quantum ...
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1 vote
1 answer
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How to construct Deutsch-Josza using CX and Hadamard gates?

How can I construct Deutsch-Josza? I know that I need superposition and phase kickback, which means I need to apply Hadamard Gate at the beginning the at the end, I also need to apply an $X$ gate then ...
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2 votes
1 answer
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How to build an algorithm with quantum circuits to calculate the outer product of two states?

I want to directly use quantum circuits or quantum algorithms to obtain the outer product of $U_A|a\rangle$ (it is a column vector) and another column vector $U_B|b\rangle$, what are the reference ...
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0 votes
1 answer
75 views

Calculating the expectation value of an observable in Qiskit

Consider the following quantum circuit that consists of a three qubit quantum register and an ancilla qubit: Let $W$ and $V$ be unitary operators. $U(t)$ is an implementation of unitary time ...
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5 votes
1 answer
120 views

Construction of unitary matrices built from linear combination of Pauli strings

Let's define $P_k \in \{ I, X, Y, Z \}^{\otimes n}$ and called each of these $P_k$ as a Pauli string (or word) then given that $$U = \sum_{k=1}^L c_kP_k $$ with the following conditions: $\sum_{k=1}...
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3 votes
0 answers
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Clarifying basis encoding

Background I'm reviewing basis encoding in this paper. In their example, they state: $(-.07, 0.1, 0.2)^T \in \mathbb{R}^3$ is encoded as $|x\rangle = |11011\;01011\;00011\rangle$ Unpacking this, it ...
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1 vote
0 answers
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What is the relation between the database made up of N elements and the index made up of a string length n in the query model?

I am working on a circuit model that contains a blackbox (query) and do not understand the relationship between what is in the black box and the way we get out the value of the element we index. The ...
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0 votes
0 answers
75 views

How can I solve problems with quantum computers ? (Methodology)

I am reading these days a book about programming quantum computing using the language Silq. I reached half the Silq book. The good thing about the Silq book is that it teaches the mathematics of ...
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3 votes
1 answer
88 views

Databases for Quantum Computing & Quantum Computers - Do we need to create new databases?

Recently, I asked a question about programming languages that can be compatible with quantum computers. Link to the question here: Will standard programming languages be applicable for quantum ...
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0 votes
1 answer
140 views

Hybrid Quantum LSTM in Qiskit

I read this article on a Hybrid Quantum LSTM in Pennylane and I'm trying to replicate it in Qiskit. Nevertheless it doesn't seem to work very well. Here's my code ...
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3 votes
1 answer
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Grover's algorithm: Rotation in opposite direction

In Grover's algorithm we have the solution superposition $|\omega\rangle$ and the non-solution superposition $|s'\rangle$ (containing all non-solutions). Furthermore, we rotate our starting equal-...
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3 votes
0 answers
95 views

Quantum Machine Learning Masters thesis topics [closed]

I'm a prefinal year Physics Masters student looking to pursue my thesis in the domain of Quantum computing, particularly in the areas of Quantum Simulation or Quantum Machine Learning (theory/...
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4 votes
1 answer
62 views

Will standard programming languages be applicable for quantum computing?

I'm new to quantum computers and computing, so it's possible my question is pointless or unnecessary ... but what about current programming languages such as Java, C++, Python in terms of quantum ...
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1 vote
1 answer
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how to implement QSVM for full dataset [closed]

I have executed the QSVM qiskit code for breast cancer dataset given here: ...
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1 vote
1 answer
48 views

does there exist a quantum approximate cloning method that does not modify the initial qubit (the one whose state we want to clone)?

I am currently trying to implement circuit (in Qiskit if that is relevant) to approximate a state of a qubit without measuring it (basically I want to "attach it" to a qubit and have some ...
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6 votes
3 answers
240 views

Transforming a Quantum State to a superposition of its inverse [duplicate]

Does there exist a circuit that allows you to transform a quantum state into a superposition of its inverse; i.e., transform a state into an equal superposition of all basis states that are orthogonal ...
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