7,499 research outputs found
Examples of Gaussian cluster computation
We give simple examples that illustrate the principles of one-way quantum
computation using Gaussian continuous-variable cluster states. In these
examples, we only consider single-mode evolutions, realizable via linear
clusters. In particular, we focus on Gaussian single-mode transformations
performed through the cluster state. Our examples highlight the differences
between cluster-based schemes and protocols in which special quantum states are
prepared off-line and then used as a resource for the on-line computation.Comment: 15 pages, 3 figure
Universal linear Bogoliubov transformations through one-way quantum computation
We show explicitly how to realize an arbitrary linear unitary Bogoliubov
transformation (LUBO) on a multi-mode quantum state through homodyne-based
one-way quantum computation. Any LUBO can be approximated by means of a fixed,
finite-sized, sufficiently squeezed Gaussian cluster state that allows for the
implementation of beam splitters (in form of three-mode connection gates) and
general one-mode LUBOs. In particular, we demonstrate that a linear four-mode
cluster state is a sufficient resource for an arbitrary one-mode LUBO.
Arbitrary input quantum states including non-Gaussian states could be
efficiently attached to the cluster through quantum teleportation.Comment: 10 pages, 6 figure
Universal Gate Set for Continuous-Variable Quantum Computation with Microwave Circuits
We provide an explicit construction of a universal gate set for
continuous-variable quantum computation with microwave circuits. Such a
universal set has been first proposed in quantum-optical setups, but its
experimental implementation has remained elusive in that domain due to the
difficulties in engineering strong nonlinearities. Here, we show that a
realistic microwave architecture allows to overcome this difficulty. As an
application, we show that this architecture allows to generate a cubic phase
state with an experimentally feasible procedure. This work highlights a
practical advantage of microwave circuits with respect to optical systems for
the purpose of engineering non-Gaussian states, and opens the quest for
continuous-variable algorithms based on a few repetitions of elementary gates
from the continuous-variable universal set.Comment: 6+6 pages, 2 figure
How to decompose arbitrary continuous-variable quantum operations
We present a general, systematic, and efficient method for decomposing any
given exponential operator of bosonic mode operators, describing an arbitrary
multi-mode Hamiltonian evolution, into a set of universal unitary gates.
Although our approach is mainly oriented towards continuous-variable quantum
computation, it may be used more generally whenever quantum states are to be
transformed deterministically, e.g. in quantum control, discrete-variable
quantum computation, or Hamiltonian simulation. We illustrate our scheme by
presenting decompositions for various nonlinear Hamiltonians including quartic
Kerr interactions. Finally, we conclude with two potential experiments
utilizing offline-prepared optical cubic states and homodyne detections, in
which quantum information is processed optically or in an atomic memory using
quadratic light-atom interactions.Comment: Ver. 3: published version with supplementary materia
Hybrid quantum information processing
The development of quantum information processing has traditionally followed
two separate and not immediately connected lines of study. The main line has
focused on the implementation of quantum bit (qubit) based protocols whereas
the other line has been devoted to implementations based on high-dimensional
Gaussian states (such as coherent and squeezed states). The separation has been
driven by the experimental difficulty in interconnecting the standard
technologies of the two lines. However, in recent years, there has been a
significant experimental progress in refining and connecting the technologies
of the two fields which has resulted in the development and experimental
realization of numerous new hybrid protocols. In this Review, we summarize
these recent efforts on hybridizing the two types of schemes based on discrete
and continuous variables.Comment: 13 pages, 6 figure
Simulation of the elementary evolution operator with the motional states of an ion in an anharmonic trap
Following a recent proposal of L. Wang and D. Babikov, J. Chem. Phys. 137,
064301 (2012), we theoretically illustrate the possibility of using the
motional states of a ion trapped in a slightly anharmonic potential to
simulate the single-particle time-dependent Schr\"odinger equation. The
simulated wave packet is discretized on a spatial grid and the grid points are
mapped on the ion motional states which define the qubit network. The
localization probability at each grid point is obtained from the population in
the corresponding motional state. The quantum gate is the elementary evolution
operator corresponding to the time-dependent Schr\"odinger equation of the
simulated system. The corresponding matrix can be estimated by any numerical
algorithm. The radio-frequency field able to drive this unitary transformation
among the qubit states of the ion is obtained by multi-target optimal control
theory. The ion is assumed to be cooled in the ground motional state and the
preliminary step consists in initializing the qubits with the amplitudes of the
initial simulated wave packet. The time evolution of the localization
probability at the grids points is then obtained by successive applications of
the gate and reading out the motional state population. The gate field is
always identical for a given simulated potential, only the field preparing the
initial wave packet has to be optimized for different simulations. We check the
stability of the simulation against decoherence due to fluctuating electric
fields in the trap electrodes by applying dissipative Lindblad dynamics.Comment: 31 pages, 8 figures. Revised version. New title, new figure and new
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