QuEST

A multithreaded, distributed, GPU-accelerated simulator of quantum computers

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README

<div align="center">  <a href="https://quest.qtechtheory.org"> <img src="https://raw.githubusercontent.com/QuEST-Kit/QuEST/refs/heads/main/utils/docs/logos/banner.png" alt="The QuEST logo" width=400> </a>

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The Quantum Exact Simulation Toolkit (QuEST) is a high-performance simulator of quantum statevectors and density matrices. It hybridises multithreading, GPU acceleration and distribution to run lightning fast on laptops, desktops and supercomputers, parallelising over multiple cores, CPUs and GPUs. Behind the scenes, QuEST leverages OpenMP, MPI, CUDA, HIP, Thrust, cuQuantum and GPUDirect for cutting-edge performance on modern multi-GPU clusters, and compatibility with older NVIDIA and AMD GPUs. These deployments can be combined in any combination, or automatically decided at runtime, yet are abstracted behind a single, seamless interface, accessible by both C and C++ and all the major compilers (detailed here).

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As of v4.2, QuEST development is led by the EPCC team at the University of Edinburgh, with support and former development by the QTechTheory group at the University of Oxford. QuEST has also received contributions and support from the below organisations. In particular, QuEST v4.0 was made possible through the support of the UK National Quantum Computing centre (NQCC200921) and the UKRI SEEQA project.

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To learn more:

view the <a href="#main_documentation">documentation</a>
visit the website
read the whitepaper, which featured in Scientific Report's Top 100 in Physics :trophy:

🎉 Introduction

QuEST has a simple interface which is agnostic to whether it's running on CPUs, GPUs or a networked supercomputer.

Qureg qureg = createQureg(30);
initRandomPureState(qureg);

applyHadamard(qureg, 0);
applyControlledRotateX(qureg, 0, 1, angle);
applyFullQuantumFourierTransform(qureg);

reportQureg(qureg);

qreal prob  = calcProbOfQubitOutcome(qureg, 0, outcome);
qreal expec = calcExpecPauliStr(qureg, getPauliStr("XYZ"));

Yet, it is flexible

mixDepolarising(qureg, targ, prob);
mixKrausMap(qureg, targs, ntargs, krausmap);

applyQubitMeasurement(qureg, targ);
applyMultiQubitProjector(qureg, targs, outcomes, ntargs);

applyControlledPauliGadget(qureg, ctrl, paulistr, angle);
applyMultiStateControlledSwap(qureg, ctrls, states, nctrls, targ1, targ2);

leftapplyCompMatr1(qureg, targ, getInlineCompMatr1( {{1,2i},{3i,4}} ));
leftapplyDiagMatrPower(qureg, targs, ntargs, diagmatr, exponent);

and extremely powerful

setFullStateDiagMatrFromMultiVarFunc(fullmatr, myfunc, ntargsPerVar, nvars);
applyFullStateDiagMatrPower(qureg, fullmatr, exponent);

CompMatr matr = createCompMatr(10);
setCompMatr(matr, ...);
applyCompMatr(qureg, targs, 10, matr);

PauliStrSum observ = createInlinePauliStrSum(R"(
    0.123 XXIXX
    1.23i XYZXZ
    -1-6i IIZII
)");
applyTrotterizedPauliStrSumGadget(qureg, observ, time, order, nreps);

Qureg reduce = calcPartialTrace(qureg, targs, ntargs);
qreal expec1 = calcExpecPauliStrSum(reduce, observ);
qreal expec2 = calcExpecFullStateDiagMatr(qureg, fullmatr);

✅ Features

QuEST supports:

☑️ density matrices for precise simulation of noisy quantum computers
☑️ general unitaries with any number of control, control-states, and target qubits
☑️ general decoherence channels of any dimension
☑️ general observables in the Pauli or diagonal-Z bases
☑️ many many operators, including Pauli gadgets, trotterised time evolutions, and projectors
☑️ many tools to analyse quantum states, such as calculations of probability, fidelity, expectation value, distances and partial traces
☑️ variable precision through qreal and qcomp numerical types which can use single, double or quad precision
☑️ direct access to amplitudes for rapid custom modification of the quantum state
☑️ native compilation on MacOS, Linux and Windows, through Clang, GNU, Intel, and MSVC compilers
☑️ hybridisation of multithreading, GPU-acceleration, distribution and GPU-distribution
☑️ optimisation using NVLink'd GPUs, cuQuantum, and CUDA-aware MPI
☑️ automatic deployment of a Qureg to the optimal hardware at runtime
☑️ hardware probing to determine how many qubits can be simulated at runtime
☑️ bespoke algorithms to optimally simulate a wide variety of esoteric operations

📖 Documentation

[!IMPORTANT] QuEST v4's documentation is still under construction!

Visit the docs for guides and tutorials, or the API which is divided into:

<!-- You can also browse QuEST's extensive [tests](https://quest-kit.github.io/QuEST/group__tests.html): - [test utilities](https://quest-kit.github.io/QuEST/group__testutils.html) - [cache](https://quest-kit.github.io/QuEST/group__testutilscache.html) - [compare](https://quest-kit.github.io/QuEST/group__testutilscompare.html) - [conve

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