210 research outputs found
A cryogenic surface-electrode elliptical ion trap for quantum simulation
Two-dimensional crystals of trapped ions are a promising system with which to
implement quantum simulations of challenging problems such as spin frustration.
Here, we present a design for a surface-electrode elliptical ion trap which
produces a 2-D ion crystal and is amenable to microfabrication, which would
enable higher simulated coupling rates, as well as interactions based on
magnetic forces generated by on-chip currents. Working in an 11 K cryogenic
environment, we experimentally verify to within 5% a numerical model of the
structure of ion crystals in the trap. We also explore the possibility of
implementing quantum simulation using magnetic forces, and calculate J-coupling
rates on the order of 10^3 / s for an ion crystal height of 10 microns, using a
current of 1 A
Using Quantum Computers for Quantum Simulation
Numerical simulation of quantum systems is crucial to further our
understanding of natural phenomena. Many systems of key interest and
importance, in areas such as superconducting materials and quantum chemistry,
are thought to be described by models which we cannot solve with sufficient
accuracy, neither analytically nor numerically with classical computers. Using
a quantum computer to simulate such quantum systems has been viewed as a key
application of quantum computation from the very beginning of the field in the
1980s. Moreover, useful results beyond the reach of classical computation are
expected to be accessible with fewer than a hundred qubits, making quantum
simulation potentially one of the earliest practical applications of quantum
computers. In this paper we survey the theoretical and experimental development
of quantum simulation using quantum computers, from the first ideas to the
intense research efforts currently underway.Comment: 43 pages, 136 references, review article, v2 major revisions in
response to referee comments, v3 significant revisions, identical to
published version apart from format, ArXiv version has table of contents and
references in alphabetical orde
High threshold distributed quantum computing with three-qubit nodes
In the distributed quantum computing paradigm, well-controlled few-qubit
`nodes' are networked together by connections which are relatively noisy and
failure prone. A practical scheme must offer high tolerance to errors while
requiring only simple (i.e. few-qubit) nodes. Here we show that relatively
modest, three-qubit nodes can support advanced purification techniques and so
offer robust scalability: the infidelity in the entanglement channel may be
permitted to approach 10% if the infidelity in local operations is of order
0.1%. Our tolerance of network noise is therefore a order of magnitude beyond
prior schemes, and our architecture remains robust even in the presence of
considerable decoherence rates (memory errors). We compare the performance with
that of schemes involving nodes of lower and higher complexity. Ion traps, and
NV- centres in diamond, are two highly relevant emerging technologies.Comment: 5 figures, 12 pages in single column format. Revision has more
detailed comparison with prior scheme
QuTiP: An open-source Python framework for the dynamics of open quantum systems
We present an object-oriented open-source framework for solving the dynamics
of open quantum systems written in Python. Arbitrary Hamiltonians, including
time-dependent systems, may be built up from operators and states defined by a
quantum object class, and then passed on to a choice of master equation or
Monte-Carlo solvers. We give an overview of the basic structure for the
framework before detailing the numerical simulation of open system dynamics.
Several examples are given to illustrate the build up to a complete
calculation. Finally, we measure the performance of our library against that of
current implementations. The framework described here is particularly
well-suited to the fields of quantum optics, superconducting circuit devices,
nanomechanics, and trapped ions, while also being ideal for use in classroom
instruction.Comment: 16 pages, 12 figure
A Quantum-Quantum Metropolis Algorithm
Recently, the idea of classical Metropolis sampling through Markov chains has
been generalized for quantum Hamiltonians. However, the underlying Markov chain
of this algorithm is still classical in nature. Due to Szegedy's method, the
Markov chains of classical Hamiltonians can achieve a quadratic quantum speedup
in the eigenvalue gap of the corresponding transition matrix. A natural
question to ask is whether Szegedy's quantum speedup is merely a consequence of
employing classical Hamiltonians, where the eigenstates simply coincide with
the computational basis, making cloning of the classical information possible.
We solve this problem by introducing a quantum version of the method of
Markov-chain quantization combined with the quantum simulated annealing (QSA)
procedure, and describe explicitly a novel quantum Metropolis algorithm, which
exhibits a quadratic quantum speedup in the eigenvalue gap of the corresponding
Metropolis Markov chain for any quantum Hamiltonian. This result provides a
complete generalization of the classical Metropolis method to the quantum
domain.Comment: 7 page
Efficient Algorithms for Universal Quantum Simulation
A universal quantum simulator would enable efficient simulation of quantum
dynamics by implementing quantum-simulation algorithms on a quantum computer.
Specifically the quantum simulator would efficiently generate qubit-string
states that closely approximate physical states obtained from a broad class of
dynamical evolutions. I provide an overview of theoretical research into
universal quantum simulators and the strategies for minimizing computational
space and time costs. Applications to simulating many-body quantum simulation
and solving linear equations are discussed
Hole burning in a nanomechanical resonator coupled to a Cooper pair box
We propose a scheme to create holes in the statistical distribution of
excitations of a nanomechanical resonator. It employs a controllable coupling
between this system and a Cooper pair box. The success probability and the
fidelity are calculated and compared with those obtained in the atom-field
system via distinct schemes. As an application we show how to use the
hole-burning scheme to prepare (low excited) Fock states.Comment: 7 pages, 10 figure
Bloch oscillations of quasispin polaritons in a magneto-optically controlled atomic ensemble
We consider the propagation of a quantized polarized light in a
magneto-optically manipulated atomic ensemble with a tripod configuration.
Polariton formalism is applied when the medium is subjected to a washboard
magnetic field under electromagnetically induced transparency. The dark-state
polariton with multiple components is achieved. We analyze quantum dynamics of
the dark-state polariton by some experiment data from rubidium D1-line. It is
found that one component propagates freely, however the wavepacket trajectory
of the other component performs Bloch oscillations.Comment: 6 pages, 4 figure
Coupling slot-waveguide cavities for large-scale quantum optical devices
By offering effective modal volumes significantly less than a cubic
wavelength, slot-waveguide cavities offer a new in-road into strong atom-photon
coupling in the visible regime. Here we explore two-dimensional arrays of
coupled slot cavities which underpin designs for novel quantum emulators and
polaritonic quantum phase transition devices. Specifically, we investigate the
lateral coupling characteristics of diamond-air and GaP-air slot waveguides
using numerically-assisted coupled-mode theory, and the longitudinal coupling
properties via distributed Bragg reflectors using mode-propagation simulations.
We find that slot-waveguide cavities in the Fabry-Perot arrangement can be
coupled and effectively treated with a tight-binding description, and are a
suitable platform for realizing Jaynes-Cummings-Hubbard physics.Comment: 11 pages, 7 figures, submitte
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