497 research outputs found
Advanced Simulation of Quantum Computations
Quantum computation is a promising emerging technology which, compared to
conventional computation, allows for substantial speed-ups e.g. for integer
factorization or database search. However, since physical realizations of
quantum computers are in their infancy, a significant amount of research in
this domain still relies on simulations of quantum computations on conventional
machines. This causes a significant complexity which current state-of-the-art
simulators try to tackle with a rather straight forward array-based
representation and by applying massive hardware power. There also exist
solutions based on decision diagrams (i.e. graph-based approaches) that try to
tackle the exponential complexity by exploiting redundancies in quantum states
and operations. However, these existing approaches do not fully exploit
redundancies that are actually present. In this work, we revisit the basics of
quantum computation, investigate how corresponding quantum states and quantum
operations can be represented even more compactly, and, eventually, simulated
in a more efficient fashion. This leads to a new graph-based simulation
approach which outperforms state-of-the-art simulators (array-based as well as
graph-based). Experimental evaluations show that the proposed solution is
capable of simulating quantum computations for more qubits than before, and in
significantly less run-time (several magnitudes faster compared to previously
proposed simulators). An implementation of the proposed simulator is publicly
available online at http://iic.jku.at/eda/research/quantum_simulation
Synthesis of Reversible Functions Beyond Gate Count and Quantum Cost
Many synthesis approaches for reversible and quantum logic have been proposed
so far. However, most of them generate circuits with respect to simple metrics,
i.e. gate count or quantum cost. On the other hand, to physically realize
reversible and quantum hardware, additional constraints exist. In this paper,
we describe cost metrics beyond gate count and quantum cost that should be
considered while synthesizing reversible and quantum logic for the respective
target technologies. We show that the evaluation of a synthesis approach may
differ if additional costs are applied. In addition, a new cost metric, namely
Nearest Neighbor Cost (NNC) which is imposed by realistic physical quantum
architectures, is considered in detail. We discuss how existing synthesis flows
can be extended to generate optimal circuits with respect to NNC while still
keeping the quantum cost small.Comment: 16 pages, 6 figures, 4 tables, International Workshop on Logic and
Synthesi
NISQ circuit compilation is the travelling salesman problem on a torus
Noisy, intermediate-scale quantum (NISQ) computers are expected to execute
quantum circuits of up to a few hundred qubits. The circuits have to conform to
NISQ architectural constraints regarding qubit allocation and the execution of
multi-qubit gates. Quantum circuit compilation (QCC) takes a nonconforming
circuit and outputs a compatible circuit. Can classical optimisation methods be
used for QCC? Compilation is a known combinatorial problem shown to be solvable
by two types of operations: 1) qubit allocation, and 2) gate scheduling. We
show informally that the two operations form a discrete ring. The search
landscape of QCC is a two dimensional discrete torus where vertices represent
configurations of how circuit qubits are allocated to NISQ registers. Torus
edges are weighted by the cost of scheduling circuit gates. The novelty of our
approach uses the fact that a circuit's gate list is circular: compilation can
start from any gate as long as all the gates will be processed, and the
compiled circuit has the correct gate order. By showing that QCC can be solved
as a travelling salesman problem, we bridge a theoretical and practical gap
between classical circuit design automation and the emerging field of quantum
circuit optimisation.Comment: rewritten. added torus. showing similarity with ts
An Efficient Methodology for Mapping Quantum Circuits to the IBM QX Architectures
In the past years, quantum computers more and more have evolved from an
academic idea to an upcoming reality. IBM's project IBM Q can be seen as
evidence of this progress. Launched in March 2017 with the goal to provide
access to quantum computers for a broad audience, this allowed users to conduct
quantum experiments on a 5-qubit and, since June 2017, also on a 16-qubit
quantum computer (called IBM QX2 and IBM QX3, respectively). Revised versions
of these 5-qubit and 16-qubit quantum computers (named IBM QX4 and IBM QX5,
respectively) are available since September 2017. In order to use these, the
desired quantum functionality (e.g. provided in terms of a quantum circuit) has
to be properly mapped so that the underlying physical constraints are satisfied
- a complex task. This demands solutions to automatically and efficiently
conduct this mapping process. In this paper, we propose a methodology which
addresses this problem, i.e. maps the given quantum functionality to a
realization which satisfies all constraints given by the architecture and, at
the same time, keeps the overhead in terms of additionally required quantum
gates minimal. The proposed methodology is generic, can easily be configured
for similar future architectures, and is fully integrated into IBM's SDK.
Experimental evaluations show that the proposed approach clearly outperforms
IBM's own mapping solution. In fact, for many quantum circuits, the proposed
approach determines a mapping to the IBM architecture within minutes, while
IBM's solution suffers from long runtimes and runs into a timeout of 1 hour in
several cases. As an additional benefit, the proposed approach yields mapped
circuits with smaller costs (i.e. fewer additional gates are required). All
implementations of the proposed methodology is publicly available at
http://iic.jku.at/eda/research/ibm_qx_mapping
Design Automation for Adiabatic Circuits
Adiabatic circuits are heavily investigated since they allow for computations
with an asymptotically close to zero energy dissipation per operation - serving
as an alternative technology for many scenarios where energy efficiency is
preferred over fast execution. Their concepts are motivated by the fact that
the information lost from conventional circuits results in an entropy increase
which causes energy dissipation. To overcome this issue, computations are
performed in a (conditionally) reversible fashion which, additionally, have to
satisfy switching rules that are different from conventional circuitry - crying
out for dedicated design automation solutions. While previous approaches either
focus on their electrical realization (resulting in small, hand-crafted
circuits only) or on designing fully reversible building blocks (an unnecessary
overhead), this work aims for providing an automatic and dedicated design
scheme that explicitly takes the recent findings in this domain into account.
To this end, we review the theoretical and technical background of adiabatic
circuits and present automated methods that dedicatedly realize the desired
function as an adiabatic circuit. The resulting methods are further optimized -
leading to an automatic and efficient design automation for this promising
technology. Evaluations confirm the benefits and applicability of the proposed
solution
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
Synthesis of Arbitrary Quantum Circuits to Topological Assembly: Systematic, Online and Compact
It is challenging to transform an arbitrary quantum circuit into a form
protected by surface code quantum error correcting codes (a variant of
topological quantum error correction), especially if the goal is to minimise
overhead. One of the issues is the efficient placement of magic state
distillation sub circuits, so-called distillation boxes, in the space-time
volume that abstracts the computation's required resources. This work presents
a general, systematic, online method for the synthesis of such circuits.
Distillation box placement is controlled by so-called schedulers. The work
introduces a greedy scheduler generating compact box placements. The
implemented software, whose source code is available online, is used to
illustrate and discuss synthesis examples. Synthesis and optimisation
improvements are proposed
Reliable quantum circuits have defects
State of the art quantum computing architectures are founded on the decision
to use scalable but faulty quantum hardware in conjunction with an efficient
error correcting code capable of tolerating high error rates. The promised
effect of this decision is that the first large-scale practical quantum
computer is within reach. Coming to grips with the strategy and the challenges
of preparing reliable executions of an arbitrary quantum computation is not
difficult. Moreover, the article explains why defects are good.Comment: preprint of the paper from XRD
Advanced Simulation of Droplet Microfluidics
The complexity of droplet microfluidics grows by implementing parallel
processes and multiple functionalities on a single device. This poses a
challenge to the engineer designing the microfluidic networks. In today's
design processes, the engineer relies on calculations, assumptions,
simplifications, as well as his/her experiences and intuitions. In order to
validate the obtained specification of the microfluidic network, usually a
prototype is fabricated and physical experiments are conducted thus far. In
case the design does not implement the desired functionality, this prototyping
iteration is repeated - obviously resulting in an expensive and time-consuming
design process. In order to avoid unnecessary prototyping loops, simulation
methods could help to validate the specification of the microfluidic network
before any prototype is fabricated. However, state-of-the-art simulation tools
come with severe limitations, which prevent their utilization for
practically-relevant applications. More precisely, they are often not dedicated
to droplet microfluidics, cannot handle the required physical phenomena, are
not publicly available, and can hardly be extended. In this work, we present an
advanced simulation approach for droplet microfluidics which addresses these
shortcomings and, eventually, allows to simulate practically-relevant
applications. To this end, we propose a simulation framework which directly
works on the specification of the design, supports essential physical
phenomena, is publicly available, and easy to extend. Evaluations and case
studies demonstrate the benefits of the proposed simulator: While current
state-of-the-art tools were not applicable for practically-relevant
microfluidic networks, the proposed solution allows to reduce the design time
and costs e.g. of a drug screening device from one person month and USD 1200,
respectively, to just a fraction of that.Comment: preprin
Dilution with Digital Microfluidic Biochips: How Unbalanced Splits Corrupt Target-Concentration
Sample preparation is an indispensable component of almost all biochemical
protocols, and it involves, among others, making dilutions and mixtures of
fluids in certain ratios. Recent microfluidic technologies offer suitable
platforms for automating dilutions on-chip, and typically on a digital
microfluidic biochip (DMFB), a sequence of (1:1) mix-split operations is
performed on fluid droplets to achieve the target concentration factor (CF) of
a sample. An (1:1) mixing model ideally comprises mixing of two unit-volume
droplets followed by a (balanced) splitting into two unit-volume
daughter-droplets. However, a major source of error in fluidic operations is
due to unbalanced splitting, where two unequal-volume droplets are produced
following a split. Such volumetric split-errors occurring in different
mix-split steps of the reaction path often cause a significant drift in the
target-CF of the sample, the precision of which cannot be compromised in
life-critical assays. In order to circumvent this problem, several
error-recovery or error-tolerant techniques have been proposed recently for
DMFBs. Unfortunately, the impact of such fluidic errors on a target-CF and the
dynamics of their behavior have not yet been rigorously analyzed. In this work,
we investigate the effect of multiple volumetric split-errors on various
target-CFs during sample preparation. We also perform a detailed analysis of
the worst-case scenario, i.e., the condition when the error in a target-CF is
maximized. This analysis may lead to the development of new techniques for
error-tolerant sample preparation with DMFBs without using any sensing
operation.Comment: 11 pages, 17 figure
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