38 research outputs found
PAN: Pulse Ansatz on NISQ Machines
Variational quantum algorithms (VQAs) have demonstrated great potentials in
the NISQ era. In the workflow of VQA, the parameters of ansatz are iteratively
updated to approximate the desired quantum states. We have seen various efforts
to draft better ansatz with less gates. In quantum computers, the gate ansatz
will eventually be transformed into control signals such as microwave pulses on
transmons. And the control pulses need elaborate calibration to minimize the
errors such as over-rotation and under-rotation. In the case of VQAs, this
procedure will introduce redundancy, but the variational properties of VQAs can
naturally handle problems of over-rotation and under-rotation by updating the
amplitude and frequency parameters. Therefore, we propose PAN, a native-pulse
ansatz generator framework for VQAs. We generate native-pulse ansatz with
trainable parameters for amplitudes and frequencies. In our proposed PAN, we
are tuning parametric pulses, which are natively supported on NISQ computers.
Considering that parameter-shift rules do not hold for native-pulse ansatz, we
need to deploy non-gradient optimizers. To constrain the number of parameters
sent to the optimizer, we adopt a progressive way to generate our native-pulse
ansatz. Experiments are conducted on both simulators and quantum devices to
validate our methods. When adopted on NISQ machines, PAN obtained improved the
performance with decreased latency by an average of 86%. PAN is able to achieve
99.336% and 96.482% accuracy for VQE tasks on H2 and HeH+ respectively, even
with considerable noises in NISQ machines.Comment: 13 pages, 13 figure
Partial Compilation of Variational Algorithms for Noisy Intermediate-Scale Quantum Machines
Quantum computing is on the cusp of reality with Noisy Intermediate-Scale
Quantum (NISQ) machines currently under development and testing. Some of the
most promising algorithms for these machines are variational algorithms that
employ classical optimization coupled with quantum hardware to evaluate the
quality of each candidate solution. Recent work used GRadient Descent Pulse
Engineering (GRAPE) to translate quantum programs into highly optimized machine
control pulses, resulting in a significant reduction in the execution time of
programs. This is critical, as quantum machines can barely support the
execution of short programs before failing.
However, GRAPE suffers from high compilation latency, which is untenable in
variational algorithms since compilation is interleaved with computation. We
propose two strategies for partial compilation, exploiting the structure of
variational circuits to pre-compile optimal pulses for specific blocks of
gates. Our results indicate significant pulse speedups ranging from 1.5x-3x in
typical benchmarks, with only a small fraction of the compilation latency of
GRAPE.Comment: Appearing in the 52nd Annual IEEE/ACM International Symposium on
Microarchitecture (MICRO-52), October 12-16, 2019, Columbus, OH, US
Full stack development toward a trapped ion logical qubit
Quantum error correction is a key step toward the construction of a large-scale quantum computer, by preventing small infidelities in quantum gates from accumulating over the course of an algorithm. Detecting and correcting errors is achieved by using multiple physical qubits to form a smaller number of robust logical
qubits. The physical implementation of a logical qubit requires multiple qubits, on which high fidelity gates
can be performed.
The project aims to realize a logical qubit based on ions confined on a microfabricated surface trap. Each
physical qubit will be a microwave dressed state qubit based on 171Yb+ ions. Gates are intended to be realized through RF and microwave radiation in combination with magnetic field gradients. The project vertically integrates software down to hardware compilation layers in order to deliver, in the near future, a fully functional small device demonstrator.
This thesis presents novel results on multiple layers of a full stack quantum computer model. On the hardware level a robust quantum gate is studied and ion displacement over the X-junction geometry is demonstrated.
The experimental organization is optimized through automation and compressed waveform data transmission. A new quantum assembly language purely dedicated to trapped ion quantum computers is introduced. The demonstrator is aimed at testing implementation of quantum error correction codes while preparing for larger
scale iterations.Open Acces
OpenQASM 3: a broader and deeper quantum assembly language
Quantum assembly languages are machine-independent languages that traditionally describe quantum computation in the circuit model. Open quantum assembly language (OpenQASM 2) was proposed as an imperative programming language for quantum circuits based on earlier QASM dialects. In principle, any quantum computation could be described using OpenQASM 2, but there is a need to describe a broader set of circuits beyond the language of qubits and gates. By examining interactive use cases, we recognize two different timescales of quantum-classical interactions: real-time classical computations that must be performed within the coherence times of the qubits, and near-time computations with less stringent timing. Since the near-time domain is adequately described by existing programming frameworks, we choose in OpenQASM 3 to focus on the real-time domain, which must be more tightly coupled to the execution of quantum operations. We add support for arbitrary control flow as well as calling external classical functions. In addition, we recognize the need to describe circuits at multiple levels of specificity, and therefore we extend the language to include timing, pulse control, and gate modifiers. These new language features create a multi-level intermediate representation for circuit development and optimization, as well as control sequence implementation for calibration, characterization, and error mitigation
Full-Stack, Real-System Quantum Computer Studies: Architectural Comparisons and Design Insights
In recent years, Quantum Computing (QC) has progressed to the point where
small working prototypes are available for use. Termed Noisy Intermediate-Scale
Quantum (NISQ) computers, these prototypes are too small for large benchmarks
or even for Quantum Error Correction, but they do have sufficient resources to
run small benchmarks, particularly if compiled with optimizations to make use
of scarce qubits and limited operation counts and coherence times. QC has not
yet, however, settled on a particular preferred device implementation
technology, and indeed different NISQ prototypes implement qubits with very
different physical approaches and therefore widely-varying device and machine
characteristics.
Our work performs a full-stack, benchmark-driven hardware-software analysis
of QC systems. We evaluate QC architectural possibilities, software-visible
gates, and software optimizations to tackle fundamental design questions about
gate set choices, communication topology, the factors affecting benchmark
performance and compiler optimizations. In order to answer key cross-technology
and cross-platform design questions, our work has built the first top-to-bottom
toolflow to target different qubit device technologies, including
superconducting and trapped ion qubits which are the current QC front-runners.
We use our toolflow, TriQ, to conduct {\em real-system} measurements on 7
running QC prototypes from 3 different groups, IBM, Rigetti, and University of
Maryland. From these real-system experiences at QC's hardware-software
interface, we make observations about native and software-visible gates for
different QC technologies, communication topologies, and the value of
noise-aware compilation even on lower-noise platforms. This is the largest
cross-platform real-system QC study performed thus far; its results have the
potential to inform both QC device and compiler design going forward.Comment: Preprint of a publication in ISCA 201