Qrack

The open source vm6502q/qrack library and its associated plugins and projects under the vm6502q organization header comprise a framework for full-stack quantum computing development, via high performance and fundamentally optimized simulation. The intent of "Qrack" is to provide maximum performance for the simulation of an ideal, virtually error-free quantum computer, across the broadest possible set of hardware and operating systems.

Using the C++11 standard, at base, Qrack has an external-dependency-free CPU simulator "engine," as well as a GPU simulator engine that depends only on OpenCL. The QUnit layer provides novel, fundamental optimizations in the simulation algorithm, based on "Schmidt decomposition," transformation of basis, 2 qubit controlled gate buffer caching, the physical nonobservability of arbitrary global phase factors on a state vector, and many other "synergistic" and incidental points of optimization between these approaches and in addition to them. QUnit can be placed "on top" of either CPU, GPU, or hybrid engine types, and an additional QPager layer can sit between these, or in place of QUnit. Optimizations and hardware support are highly configurable, particularly at build time.

A QUnit or QEngine can be thought of as like simply a one-dimensional array of qubits, within which any qubit has the capacity to directly and fully entangle with any and all others. Bits can be manipulated on by a single bit gate at a time, or gates and higher level quantum instructions can be acted over arbitrary contiguous sets of bits. A qubit start index and a length is specified for parallel operation of gates over bits or for higher level instructions, like arithmetic on abitrary width registers. Some methods are designed for (bitwise and register-like) interface between quantum and classical bits. See the Doxygen for the purpose of gate-like and register-like functions.

Qrack has already been integrated with a MOS 6502 emulator, which demonstrates Qrack's original purpose, for use in developing chip-like quantum computer emulators. (The base 6502 emulator to which Qrack was added for that project is by Marek Karcz, many thanks to Marek! See https://github.com/makarcz/vm6502.)

A number of useful "pseudo-quantum" operations, which could not be carried out by true hardware quantum computers easily or at all, are included in the API for purposes like debugging, but also for potential speed-up, by allowing the classical emulation to leverage nonphysical exceptions to quantum logic, like by cloning a quantum state. In practice, though, quantum circuit programs might not rely on this (nonphysical) functionality at all. (The MOS 6502 emulator referenced above does not. It happens, many of these methods will not be exotic at all, to those familiar with other major quantum computing libraries. For example, notably, simply returning a full vector of probability amplitudes actually qualifies as "pseudo-quantum," in this sense.)

Qrack compiles like a library. To include in your project:

In your source code:

#include "qrack/qfactory.hpp"

On the command line, in the project directory

$ mkdir _build && cd _build && cmake .. && make all install

Instantiate a Qrack::QUnit, specifying the desired number of qubits. (Optionally, also specify the initial bit permutation state in the constructor.) QUnits can be (Schmidt) "composed" and "decomposed" with and from each other, to join and separate the representations of qubit "registers" that are not entangled at the point (de)composition. Both single quantum gate commands and register-like multi-bit commands are available.

For distributed simulation, the Qrack::QPager layer will segment a single register into a power-of-two count of equal length pages, running on an arbitrary number of OpenCL accelerators. The QPager layer also scales to arbitrarily small as well as large qubit counts, such that it can be appropriate for use on a single accelerator for small width simulations. The QPager layer is also compatible with Clifford set preamble circuits simulated with QStabilizerHybrid, as a layer over QPager, and QHybrid for CPU/GPU switching can be used as the "engine" layer under it. For Qrack in a cluster environment, we support the SnuCL and VirtualCL OpenCL virtualization layers, with OpenCL v1.1 compliant host code without required "host pointers."

For more information, compile the doxygen.config in the root folder, and then check the doc folder.

Documentation

Live version of the documentation, including API reference, can be obtained at: https://qrack.readthedocs.io/en/latest/

Community

Qrack has a community home at the Advanced Computing Topics server on Discord, at: https://discordapp.com/invite/Gj3CHDy

For help getting started with contributing, see our CONTRIBUTING.md.

test/tests.cpp

The included test/tests.cpp contains unit tests and usage examples. The unittests themselves can be executed:

    $ _build/unittest

Installing OpenCL on VMWare

Most platforms offer a standardized way of installing OpenCL. However, a method for VMWare benefits from documentation, here.

Download the AMD APP SDK
Install it.
Add symlinks for /opt/AMDAPPSDK-3.0/lib/x86_64/sdk/libOpenCL.so.1 to /usr/lib
Add symlinks for /opt/AMDAPPSDK-3.0/lib/x86_64/sdk/libamdocl64.so to /usr/lib
Make sure clinfo reports back that there is a valid backend to use (anything other than an error should be fine).
Install OpenGL headers: $ sudo apt install mesa-common-dev
Adjust the makefile to have the appropriate search paths

Installing OpenCL on Mac

While the OpenCL framework is available by default on most modern Macs, the C++ header cl.hpp is usually not. One option for building for OpenCL on Mac is to download this header file and include it in the Qrack project folder under include/OpenCL (as cl.hpp). The OpenCL C++ header can be found at the Khronos OpenCL registry:

https://www.khronos.org/registry/OpenCL/

Building and Installing Qrack on Windows

Qrack supports building on Windows, but some special configuration is required. Windows 10 usually comes with default OpenCL libraries for Intel (or AMD) CPUs and their graphics coprocessors, but NVIDIA graphics card support might require the CUDA Toolkit. The CUDA Toolkit also provides an OpenCL development environment, which is generally necessary to build Qrack.

Qrack requires the xxd command to convert its OpenCL kernel code into hexadecimal format for building. xxd is not natively available on Windows systems, but Windows executables for it are provided by sources including the Vim editor Windows port.

CMake on Windows will set up a 32-bit Visual Studio project by default, (if using Visual Studio,) whereas 64-bit will probably be typically desired. -DFPPOW=6 is used to set the systemic floating point accuracy to double, which is typically necessary for Q# accuracy tolerances. Putting together all of the above considerations, after installing the CUDA Toolkit and Vim, a typical CMake command for Windows might look like this:

    $ mkdir _build
    $ cd _build
    $ cmake -DCMAKE_GENERATOR_PLATFORM=x64 -DXXD_BIN="C:/Program Files (x86)/Vim/vim82/xxd.exe" -DFPPOW=6 ..

After CMake, the project must be built in Visual Studio. Once installed, the qrack_pinvoke DLL is compatible with the Qrack Q# runtime fork, to provide QrackSimulator.

WebAssembly (WASM) builds

By nature of its pure C++11 design, Qrack happens to offer excellent compatibility with Emscripten ("WebAssembly") projects. See the qrack.net repository for an example and qrack.net for a live demo. OpenCL GPU operation is not yet available for WASM builds. While CPU multithreading might be possible in WASM, it is advisable that pthread usage and linking is disabled for most conventional Web applications, with -DENABLE_PTHREAD=OFF in CMake:

emcmake cmake -DENABLE_RDRAND=OFF -DENABLE_PTHREAD=OFF -DUINTPOW=5 ..

-DQBCAPPOW=10 could be added to the above to support high-width stabilizer and Schmidt decomposition cases, with the appropriate build of the Boost headers for the toolchain.

Compiling to C from WASM

Arbitrary Qrack executables will not all necessarily link, at this time. However, wasm2c can generate C code from Qrack executables and modules, and some will successfully link.

For example, generate a .c module and a .h header from your build/examples directory:

wasm2c teleport.wasm -o teleport.c

Compile and link it from wabt, (though the command below assumes that wabt is already in your path).

cc -o teleport -Iwabt/wasm2c/ teleport.c wabt/wasm2c/wasm-rt-impl.c -lm

We apologize for providing an example that will not quite work. However, with emcc or cc, this is the general idea. Once the generated .c and .h file are syntactically valid, via modification of your original Qrack C++ program, then static linkage must be specified with -l, assuming appropriate libraries for static linkage are actually available. (Emscripten is under active development, and we thank its maintainers.)

Performing code coverage

    $ cd _build
    $ cmake -DENABLE_CODECOVERAGE=ON ..
    $ make -j 8 unittest
    $ ./unittest
    $ make coverage
    $ cd coverage_results
    $ python -m http.server

Changing default OpenCL device

OpenCL device(s) can be specified by index in Qrack::QInterface subclass constructors. The global default device can also be overridden with the environment variable QRACK_OCL_DEFAULT_DEVICE=n, where n is the index of the OpenCL device you want to use, as reported by the OpenCL initialization header.

Enable OpenCL device redistribution

Setting the environment variable QRACK_ENABLE_QUNITMULTI_REDISTRIBUTE to any value except a null string enables reactive load redistribution or balancing, in QUnitMulti. Otherwise, QUnitMulti only tries to balance load as opportunity arises when new separable QEngineShard instances are created.

QPager distributed simulation options

QPager attempts to smartly allocate low qubit widths for maximum performance. For wider qubit simulations, based on clinfo, you can segment your maximum OpenCL accelerator state vector page allocation into global qubits with the environment variable QRACK_SEGMENT_GLOBAL_QB=n, where n is an integer >=0. The default n is 0, meaning that maximum allocation segment of your GPU RAM is a single page. (For 1 global qubit, one segment would have 2 pages, akin to 2 single amplitudes, therefore one "global qubit," or 4 pages for n=2, because 2^2=4, etc., by exponent.)

QRACK_DEVICE_GLOBAL_QB=n, alternatively, lets the user also choose the performance "hint" for preferred global qubits per device. By default, n=2, for 2 global qubits or equivalently 4 pages per device. Despite the "hint," QPager will allocate fewer pages per OpenCL device for small-enough widths, to keep processing elements better occupied. Also, QPager will allocate more qubits than the hint, per device, if the maximum allocation segment is exceeded as specified by QRACK_SEGMENT_GLOBAL_QB.

QBinaryDecisionTree threshold option

QBinaryDecisionTree is a CPU-based optimization layer for reducing the total RAM footprint of high qubit width simulations. When used under the QUnit layer, state vector simulations are preferable for low widths, but higher qubit widths can be sometimes be accommodated only with binary decision trees. Hence, Qrack exposes the QRACK_BDT_THRESHOLD environment variable. QUnit subsystems with the QBinaryDecisionTree layer engage binary decision tree methods at any qubit width greater than the (integer) value of this environment variable. (Hence, 0 value engages binary decision trees at all widths, and 30 engages the method at 31 qubits or greater.) By default, binary decision tree methods begin at subsystems of 31 qubits or greater, if the environment variable is not set.

Build and environment options for CPU engines

QEngineCPU and QHybrid batch work items in groups of 2^PSTRIDEPOW before dispatching them to single CPU threads, potentially greatly reducing waiting on mutexes without signficantly hurting utilization and scheduling. The default for this option can be controlled at build time, by passing -DPSTRIDEPOW=n to CMake, with "n" being an integer greater than or equal to 0. This can be overridden at run time by the enviroment variable QRACK_PSTRIDEPOW=n. If an environment variable is not defined for this option, the default from CMake build will be used. (The default is meant to work well across different typical consumer systems, but it might benefit from system-tailored tuning via the environment variable.)

-DENABLE_QUNIT_CPU_PARALLEL=OFF disables asynchronous dispatch of QStabilizerHybrid and low width QEngineCPU/QHybrid gates with std::future. This option is on by default. Typically, QUnit stays safely under maximum thread count limits, but situations arise where async CPU simulation causes QUnit to dispatch too many CPU threads for the operating system. This build option can also reduce overall thread usage when Qrack user code operates in a multi-threaded or multi-shell environment. (Linux thread count limits might be smaller than Windows.)

Maximum allocation guard

Set the maximum allowed allocation (in MB) for the global OpenCL pool with QRACK_MAX_ALLOC_MB. This includes (VRAM) state vectors and auxiliary buffers larger than approximately sizeof(bitCapIntOcl) * sizeof(bitCapIntOcl). This should also include out-of-place single duplication of any state vector. This does not include non-OpenCL general heap or stack allocation.

Note that this controls total direct Qrack OpenCL buffer allocation, not total Qrack library allocation. Total OpenCL buffer allocation is not fully indicative of total library allocation. In practice, experimentally observed total system allocation can be less than directly tracked OpenCL allocation amounts, and we therefore suggest not setting an environment allocation limit redundant with expectations for total available system RAM.

Approximation options

QUnit can optionally round qubit subsystems proactively or on-demand to the nearest Pauli and Bell basis eigenstates according to the QRACK_QUNIT_SEPARABILITY_THRESHOLD=[0.0 - 0.5] environment variable, with a value between 0.0 and 0.5. If a probability check under Pauli or Bell basis rotation brings a single qubit probability within parameter range of any X/Y/Z basis eigenstate, (distance from closer of 0.0 or 1.0,) then the subsystem will be rounded to that state. If the environment variable is set high enough that poles overlap, (greater than (1-1/sqrt(2))/2, approximately 0.1464466,) then QUnit will cycle through X/Y/Z Pauli bases to find the best match to a mixed or pure state.

Vectorization optimization

$ cmake -DENABLE_COMPLEX_X2=ON ..

Multiply complex numbers two at a time instead of one at a time. Requires AVX for double and SSE 1.0 for float. On by default, but can be turned off for double accuracy without the AVX requirement, or to completely remove vectorization with single float accuracy.

Random number generation options (on-chip by default)

$ cmake -DENABLE_RDRAND=OFF ..

Turn off the option to attempt using on-chip hardware random number generation, which is on by default. If the option is on, Qrack might still compile to attempt using hardware random number generation, but fall back to software generation if the RDRAND opcode is not actually available. Some systems' compilers, such as that of the Raspberry Pi 3, do not recognize the compilation flag for enabling RDRAND, in which case this option needs to be turned off.

$ cmake [-DENABLE_RDRAND=OFF] -DENABLE_DEVRAND=ON ..

Instead of RDRAND, use Linux /dev/urandom/ as the Qrack random number source. (The necessary system call will only be available on Linux systems.)

$ cmake -DSEED_DEVRAND=OFF ..

If pure software pseudo-random number generator is used, it will be seeded from /dev/random by default. -DSEED_DEVRAND=OFF will use the system clock for Mersenne twister seeding, instead of /dev/random.

Pure 32 bit OpenCL kernels (including OpenCL on Raspberry Pi 3)

$ cmake -DENABLE_PURE32=ON ..

This option is needed for certain older or simpler hardware. This removes all use of 64 bit types from the OpenCL kernels, as well as completely removing the use of SIMD intrinsics. Note that this build option theoretically supports only up to 32 qubits, whereas -DENABLE_PURE32=OFF could support up to 64 qubits, (if the memory requirements were realistically attainable for either 32-bit or 64-bit hardware, or in limited cases available for QUnit Schmidt decomposition). -DENABLE_PURE32=ON is necessary to support the VC4CL OpenCL compiler for the VideoCore GPU of the Raspberry Pi 3. (Additionally, for that platform, the RDRAND instruction is not available, and you should -DENABLE_RDRAND=OFF. VC4CL for the VideoCore GPU is currently fully supported.)

Reduced or increased coherent qubit addressing

$ cmake [-DUINTPOW=n] [-DQBCAPPOW=n] ..

Qrack uses an unsigned integer primitive for ubiquitous qubit masking operations, for "local" qubits (QEngine) and "global" qubits (QUnit and QPager). This limits the maximum qubit capacity of any coherent QInterface to the total number of bits in the global (or local) masking type. By default, a 64-bit unsigned integer is used, corresponding to a maximum of 64 qubits in any coherent QInterface (if attainable, such as in limited cases with QUnit). -DUINTPOW=n reduces the "local" masking type to 2^n bits, (ex.: for max OpenCL sub-unit or page qubit width,) which might also be important with accelerators that might not support 64-bit types. -DQBCAPPOW=n sets the maximum power of "global" qubits in "paged" or QUnit types as potentially larger than single "pages" or "sub-units," for "n" >= 5, with n=5 being 2^5=32 qubits. Large "n" is possible with the Boost big integer header. (Setting "n" the same for both build options can avoid casting between "subunit" and "global qubit" masking types, if larger "paging" or QUnit widths than QEngine types are not needed.)

Variable floating point precision

$ cmake [-DFPPOW=n] ..

Like for unsigned integer masking types, this sets the floating point accuracy for state vectors to n^2. By default n=5, for 2^5=32 bit floating point precision. "half" and "double" availability depend on the system, but n=6 for "double" is commonly supported on modern hardware. n=4 for half is supported by GCC on ARM, header-only on x86_64, and by device pragma if available for OpenCL kernels.

Precompiled OpenCL kernels

$ qrack_cl_compile [path]

Precompile the OpenCL programs for all available devices, and save them to the optional "path" parameter location. By default, programs will be saved to a folder in the "home" directory, such as ~/.qrack/ on most Linux systems. (The default path can also be specified as an environment variable, QRACK_OCL_PATH.) Also by default, Qrack will attempt to load precompiled binaries from the same path, but the library will fall back to JIT compilation if program binaries are not available or are corrupt. To turn off default loading of binaries, one can simply delete the programs from this folder.

The option to load and save precompiled binaries, and where to load them from, can be controlled with the initializing method of Qrack::OCLEngine:

Qrack::OCLEngine::InitOCL(true, true, Qrack::OCLEngine::GetDefaultBinaryPath());

To use this method directly, it needs to be called before any OpenCL simulators are created in the program, as initialization happens automatically upon creating any OpenCL simulator instance. Calling the OCLEngine::InitOCL() method directly also ensures that the singleton instance has been created, with the results of the initialization call. The initialization method prototype is as follows:

/// Initialize the OCL environment, with the option to save the generated binaries. Binaries will be saved/loaded from the folder path "home".
static void InitOCL(bool buildFromSource = false, bool saveBinaries = false, std::string home = "*");

The home argument default indicates that the default home directory path should be used.

VM6502Q

$ cmake -DENABLE_VM6502Q_DEBUG=ON ..

Qrack was originally written so that the disassembler of VM6502Q should show the classical expecation value of registers, following Ehrenfest's theorem. However, this incurs significant additional overhead for QInterface::IndexedLDA(), QInterface::IndexedADC(), and QInterface::IndexedSBC(). As such, this behavior in the VM6502Q disassembler is only supported when this CMake flag is specifically enabled. (It is off by default.) These three methods will return 0, if the flag is disabled.

Turn on/off optional API components

$ cmake -DENABLE_BCD=OFF -DENABLE_REG_GATES=OFF -DENABLE_ROT_API=OFF -DENABLE_ALU=ON ..

Prior to the Qrack v7 API, a larger set of convenience methods were included in all builds, which increased the size of the library binary. By default, ENABLE_REG_GATES, ENABLE_ROT_API and ENABLE_BCD all default to OFF, while ENABLE_ALU for arithmetic logic unit methods defaults to ON.

ENABLE_REG_GATES adds various looped-over-width gates to the API, like the lengthwise CNOT(control, target, length) method. This method is a convenience wrapper on a loop of CNOT operations for length, starting from control and target, to control + length - 1 and target + length - 1. These methods were seen as opportunities for optimization, at a much earlier point, but they have fallen out of internal use, and basically none of them are optimized as special cases, anymore. Disabling ENABLE_REG_GATES does not remove lengthwise X(target, length) and H(target, length) methods, as these specific convenience methods are still commonly used in the protected API, for negating or superposing across register width.

ENABLE_ROT_API adds many less common rotation methods to the API, like dyadic fraction rotations. These never found common use in the protected API, while they add significant size to compiled binaries.

"BCD" arithmetic ("binary coded decimal") is necessary to support emulation based on the MOS-6502. However, this is an outmoded form of binary arithmetic for most or all conceivable purposes for which one would want a quantum computer. (It stores integers as base 10 digits, in binary.) Off by default, turning this option on will slightly increase binary size by including BCD ALU operations from the API, but this is necessary to support the VM6502Q chip-like emulator project.

Copyright, License, and Acknowledgements

Daniel Strano would like to specifically note that Benn Bollay is almost entirely responsible for the initial implementation of QUnit and tooling, including unit tests, in addition to large amounts of work on the documentation and many other various contributions in intensive reviews. Also, thank you to Marek Karcz for supplying an awesome base classical 6502 emulator for proof-of-concept. For unit tests and benchmarks, Qrack uses Catch v2.13.7 under the Boost Software License, Version 1.0. The QStabilizer partial simulator "engine" is adapted from CHP by Scott Aaronson, for non-commercial use. Half precision floating point headers are provided by http://half.sourceforge.net/, with our thanks. GitHub user paniash has kindly contributed README.md styling and standardization. Thank you to all our PR contributors, tracked in GitHub, and thank you to the OSS community in general for supporting code, including Adam Kelly and the qulacs team, for Qiskit and Cirq interfaces. (Additionally, the font for the Qrack logo is "Electrickle," distributed as "Freeware" from https://www.fontspace.com/fontastic/electrickle.)

We thank the Unitary Fund for its generous support, in a project to help standardize benchmarks across quantum computer simulator software! Thank you to any and all contributors!

Licensed under the GNU Lesser General Public License V3.

See LICENSE.md in the project root or https://www.gnu.org/licenses/lgpl-3.0.en.html for details.

00mjk / qrack Goto Github PK

qrack's Introduction