# 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.

1,169 questions
Filter by
Sorted by
Tagged with
1 vote
36 views

### 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 ...
1 vote
67 views

### An unexpected result of the Implementation of a finding minimum values algorithm using a qRAM

Motivated by the article Quantum algorithm for finding minimum values in a Quantum Random Access Memory, I'm training to implement a simplified version of the proposed algorithm. But the output isn't ...
• 11
109 views

### What is the initial state in the second register in Shor's algorithm?

Following up on this question, can someone help me clear up the notation we're using for states in Shor's algorithm? It's very unclear what the sentence "where the second register is $|1\rangle$ ...
85 views

### Complexity of the quantum circuits that are needed to implement communication protocol?

Consider the following simultaneous communication problem. Alice and Bob do not share any entanglement or any common randomness, and cannot communicate directly with each other. As inputs, x is given ...
106 views

### Quantum computation of classical Fisher information

Consider a pure $n$-qubit quantum state $|\psi_\theta\rangle$ prepared by some parametrized quantum circuit. There exist well-known algorithms to efficiently estimate the quantum Fisher information ...
• 23
109 views

### Can D-Wave presently solve real-world problems that conventional computers cannot solve?

There are number of threads on this site about the ability of QCs solving real-world problems (see for example What are the practical applications of quantum computing in engineering by the year 2030?,...
• 85
44 views

### How to calculate number of qubits required for Grover Algorithm while constructing it's oracle and diffuser for any Specific Algorithm or Hash?

I am reading a paper titled, " (Towards Post-Quantum Secure Symmetric Cryptography: A Mathematical Perspective)". Here, I am able to understand the gate counts and T-depth calculations. ...
163 views

692 views

### How are quantum algorithms devised?

This is a soft question, but I find it to be a very pertinent one... Algorithms for Grover's search and Simon's problems seem to come completely out of the blue, and I find it very hard to understand ...
331 views

### How do we measure the probability of outcomes in a quantum computer if qubits collapse when measured?

I understand the idea behind Quantum Computing being that we superpose all possible states of a system of qubits and amplify the probabilities of whatever it is that we want depending on the circuit ...
• 89
1 vote
109 views

### General Grover's search showing wrong results on a particular instance

I am trying to implement a general Grover's search for n qubits searching for m marked elements. I happened to observe that for ...
• 43
72 views

### Is there something like error-suppression codes?

My question is a bit on the soft side, and basically asks if there is something between error mitigation and full error correction? On the one hand, as far as I understand, trying to increase the ...
• 1,605
1 vote
82 views

### Heuristics on Quantum computers

I found the article : Strengths and Weaknesses of Quantum Computing, 1997 Charles H. Bennett, Ethan Bernstein, Gilles Brassard, Umesh Vazirani As far as I understand, this one states that quantum ...
• 131
1 vote
120 views

### Why can Shor code fix arbitrary errors?

This is taken from Page 434 of Nielsen and Chuang: To simplify the analysis, suppose noise of an arbitrary type is occurring on the first qubit only; we’ll come back to what happens when noise is ...
55 views

• 41
58 views

### GPU Support for Qiskit's SPSA Optimization Algorithm

I am using Qiskit's SPSA optimization algorithm to find the ground state energy of various lattices (fermi-Hubbard model) by running different circuits through it and having the algorithm modify the ...
136 views

### 4-cities traveling salesman quantum algorithm (QUBO)

A quantum version of the traveling salesman algorithm is discussed here: There is a reference to QUBO, Ising, and some matrix constructions, and the output in the end: Is anyone able to run through ...
• 491
279 views

### What is period finding useful for in Shor's algorithm?

Could someone help me to understand the concept behind period finding in Shor algorithm?. I'm a beginner in quantum computing. I want to know why we use Shor's algorithm to find the period and what is ...
1 vote
19 views

### How does Functional Completeness look like in the quantum world?

Can Post's theorem help to elucidate the nature of quantum logic or other non-classical logics? Quantum logic uses a different set of logical connectives than classical logic, which makes questions of ...
• 111