Introduction

hQuest is a simulation tool for quantum computation development in Haskell, using QuEST as its backend

hQuest is a very thin layer of wrapper using runtime idea. Specifically, we wrote a simple cpp script to build a runtime using QuEST, the runtime receives sequences of quantum instructions(in bytecode) as input, perform simulation using QuEST and output the results. We then FFI the interface of the runtime(as a shared library) into Haskell, with a simple parser to parse the txt file(for example, ./data/example.qcis) and then pass the resulting bytecode into runtime.

Dependency

we need haskell together with its building system cabal, both can be obtained easily following the guidance of ghcup

we also need g++ (>= 9.4.0) installed

the build script is written in racket, a dialect of lisp(you do not need to learn it, you can just use the build script as a command-line tool), which could be easily installed in ubuntu through apt-get:

sudo apt-get install racket

build

to build, firstly, update submodule:

git submodule update --init --recursive

then

• build with multicore cpus

cd quest-rt && racket build.rkt && cd -

• build with cuda support

cd quest-rt && racket build.rkt --cuda && cd -

to test

just run

LD_LIBRARY_PATH="./hquest/lib" cabal run hquest -- data/example.qcis data/example.res

where

• data/example.qcis is our input file, in QCIS format
• data/example.res contains the resulting measurement bitstring, where each measurement is triggered by QCIS M gate.

QCIS format

file format

QCIS file should be suffixed with .qcis

QAgent

QCIS is a hardware level description language(or so-called quantum assembly language), thus it contains QAgent instead of Qubit.

QAgent could be Qubit(data qubit), Coupler, Readout, Amplifier et al. For hQuest, we only need Qubit and Coupler.

Gate

Gate follows the format

<gate> *<qagent> *<parameters>

example:

XY Q02 0.5
M Q02
M Q03 Q04

where

• Qubit starts with Q
• Coupler starts with G
• Readout starts with R
• Amplifier starts with A

QCIS extension

to support more complex behavior of quantum simulator backend(such as hQuest), we need some extension to QCIS format.

• defkraus is used to declare a kraus operator, and bind it to a name

defkraus K1 2x2 [[0.7071067811865476+0j, 0+0j], [0+0j, 0.7071067811865476+0j]]

• Kraus is used to declare a quantum channel on the target qubit, using the kraus operator declared previously using defkraus

defkraus K1 2x2 [[0.7071067811865476+0j, 0+0j], [0+0j, 0.7071067811865476+0j]]
defkraus K2 2x2 [[0+0j, 0.7071067811865476+0j], [0.7071067811865476+0j, 0+0j]] 
Kraus Q01 K1 K2

Comment block

to comment out code block in .qcis file, use \\ for single line and (**) for multiple lines.

example:

X Q01
Y Q02
XY Q02 0.5
XY Q03 0.5
\\ defkraus K1 2x2 [[0.7071067811865476+0j, 0+0j], [0+0j, 0.7071067811865476+0j]]
\\ defkraus K2 2x2 [[0+0j, 0.7071067811865476+0j], [0.7071067811865476+0j, 0+0j]] 
\\ Kraus Q01 K1 K2
M Q02
M Q01
M Q03

will comment out defkraus and Kraus lines.

X Q01
Y Q02
XY Q02 0.5
XY Q03 0.5
(* 
defkraus K1 2x2 [[0.7071067811865476+0j, 0+0j], [0+0j, 0.7071067811865476+0j]]
defkraus K2 2x2 [[0+0j, 0.7071067811865476+0j], [0.7071067811865476+0j, 0+0j]] 
Kraus Q01 K1 K2
*)
M Q02
M Q01
M Q03

works the same way.