2,362 research outputs found
Online Scheduled Execution of Quantum Circuits Protected by Surface Codes
Quantum circuits are the preferred formalism for expressing quantum
information processing tasks. Quantum circuit design automation methods mostly
use a waterfall approach and consider that high level circuit descriptions are
hardware agnostic. This assumption has lead to a static circuit perspective:
the number of quantum bits and quantum gates is determined before circuit
execution and everything is considered reliable with zero probability of
failure. Many different schemes for achieving reliable fault-tolerant quantum
computation exist, with different schemes suitable for different architectures.
A number of large experimental groups are developing architectures well suited
to being protected by surface quantum error correcting codes. Such circuits
could include unreliable logical elements, such as state distillation, whose
failure can be determined only after their actual execution. Therefore,
practical logical circuits, as envisaged by many groups, are likely to have a
dynamic structure. This requires an online scheduling of their execution: one
knows for sure what needs to be executed only after previous elements have
finished executing. This work shows that scheduling shares similarities with
place and route methods. The work also introduces the first online schedulers
of quantum circuits protected by surface codes. The work also highlights
scheduling efficiency by comparing the new methods with state of the art static
scheduling of surface code protected fault-tolerant circuits.Comment: accepted in QI
Resource Optimized Quantum Architectures for Surface Code Implementations of Magic-State Distillation
Quantum computers capable of solving classically intractable problems are
under construction, and intermediate-scale devices are approaching completion.
Current efforts to design large-scale devices require allocating immense
resources to error correction, with the majority dedicated to the production of
high-fidelity ancillary states known as magic-states. Leading techniques focus
on dedicating a large, contiguous region of the processor as a single
"magic-state distillation factory" responsible for meeting the magic-state
demands of applications. In this work we design and analyze a set of optimized
factory architectural layouts that divide a single factory into spatially
distributed factories located throughout the processor. We find that
distributed factory architectures minimize the space-time volume overhead
imposed by distillation. Additionally, we find that the number of distributed
components in each optimal configuration is sensitive to application
characteristics and underlying physical device error rates. More specifically,
we find that the rate at which T-gates are demanded by an application has a
significant impact on the optimal distillation architecture. We develop an
optimization procedure that discovers the optimal number of factory
distillation rounds and number of output magic states per factory, as well as
an overall system architecture that interacts with the factories. This yields
between a 10x and 20x resource reduction compared to commonly accepted single
factory designs. Performance is analyzed across representative application
classes such as quantum simulation and quantum chemistry.Comment: 16 pages, 14 figure
Noise-Adaptive Compiler Mappings for Noisy Intermediate-Scale Quantum Computers
A massive gap exists between current quantum computing (QC) prototypes, and
the size and scale required for many proposed QC algorithms. Current QC
implementations are prone to noise and variability which affect their
reliability, and yet with less than 80 quantum bits (qubits) total, they are
too resource-constrained to implement error correction. The term Noisy
Intermediate-Scale Quantum (NISQ) refers to these current and near-term systems
of 1000 qubits or less. Given NISQ's severe resource constraints, low
reliability, and high variability in physical characteristics such as coherence
time or error rates, it is of pressing importance to map computations onto them
in ways that use resources efficiently and maximize the likelihood of
successful runs.
This paper proposes and evaluates backend compiler approaches to map and
optimize high-level QC programs to execute with high reliability on NISQ
systems with diverse hardware characteristics. Our techniques all start from an
LLVM intermediate representation of the quantum program (such as would be
generated from high-level QC languages like Scaffold) and generate QC
executables runnable on the IBM Q public QC machine. We then use this framework
to implement and evaluate several optimal and heuristic mapping methods. These
methods vary in how they account for the availability of dynamic machine
calibration data, the relative importance of various noise parameters, the
different possible routing strategies, and the relative importance of
compile-time scalability versus runtime success. Using real-system
measurements, we show that fine grained spatial and temporal variations in
hardware parameters can be exploited to obtain an average x (and up to
x) improvement in program success rate over the industry standard IBM
Qiskit compiler.Comment: To appear in ASPLOS'1
Large Scale Modular Quantum Computer Architecture with Atomic Memory and Photonic Interconnects
The practical construction of scalable quantum computer hardware capable of
executing non-trivial quantum algorithms will require the juxtaposition of
different types of quantum systems. We analyze a modular ion trap quantum
computer architecture with a hierarchy of interactions that can scale to very
large numbers of qubits. Local entangling quantum gates between qubit memories
within a single register are accomplished using natural interactions between
the qubits, and entanglement between separate registers is completed via a
probabilistic photonic interface between qubits in different registers, even
over large distances. We show that this architecture can be made
fault-tolerant, and demonstrate its viability for fault-tolerant execution of
modest size quantum circuits
Numerical and analytical studies of quantum error correction
A reliable large-scale quantum computer, if built, can solve many real-life problems exponentially faster than the existing digital devices. The biggest obstacle to building one is that they are extremely sensitive and error-prone regardless of the selection of physical implementation. Both data storage and data manipulation require careful implementation and precise control due to its quantum mechanical nature. For the development of a practical and scalable computer, it is essential to identify possible quantum errors and reduce them throughout every layer of the hierarchy of quantum computation.
In this dissertation, we present our investigation into new methods to reduce errors in quantum computers from three different directions: quantum memory, quantum control, and quantum error correcting codes. For quantum memory, we pursue the potential of the quantum equivalent of a magnetic hard drive using two-body-interaction structures in fractal dimensions. With regard to quantum control, we show that it is possible to arbitrarily reduce error when manipulating multiple quantum bits using a technique popular in nuclear magnetic resonance. Finally, we introduce an efficient tool to study quantum error correcting codes and present analysis of the codes' performance on model quantum architectures.Ph.D
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