26 research outputs found
Experimental generation of four-mode continuous-variable cluster states
Continuous-variable Gaussian cluster states are a potential resource for
universal quantum computation. They can be efficiently and unconditionally
built from sources of squeezed light using beam splitters. Here we report on
the generation of three different kinds of continuous-variable four-mode
cluster states. In our realization, the resulting cluster-type correlations are
such that no corrections other than simple phase-space displacements would be
needed when quantum information propagates through these states. At the same
time, the inevitable imperfections from the finitely squeezed resource states
and from additional thermal noise are minimized, as no antisqueezing components
are left in the cluster states.Comment: 5 pages, 4 figure
Noise analysis of single-qumode Gaussian operations using continuous-variable cluster states
We consider measurement-based quantum computation that uses scalable
continuous-variable cluster states with a one-dimensional topology. The
physical resource, known here as the dual-rail quantum wire, can be generated
using temporally multiplexed offline squeezing and linear optics or by using a
single optical parametric oscillator. We focus on an important class of quantum
gates, specifically Gaussian unitaries that act on single modes, which gives
universal quantum computation when supplemented with multi-mode operations and
photon-counting measurements. The dual-rail wire supports two routes for
applying single-qumode Gaussian unitaries: the first is to use traditional
one-dimensional quantum-wire cluster-state measurement protocols. The second
takes advantage of the dual-rail quantum wire in order to apply unitaries by
measuring pairs of qumodes called macronodes. We analyze and compare these
methods in terms of the suitability for implementing single-qumode Gaussian
measurement-based quantum computation.Comment: 25 pages, 9 figures, more accessible to general audienc
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
Demonstration of a Controlled-Phase Gate for Continuous-Variable One-Way Quantum Computation
We experimentally demonstrate a controlled-phase gate for continuous
variables in a fully measurement-based fashion. In our scheme, the two
independent input states of the gate, encoded in two optical modes, are
teleported into a four-mode Gaussian cluster state. As a result, one of the
entanglement links present in the initial cluster state appears in the two
unmeasured output modes as the corresponding entangling gate acting on the
input states. The genuine quantum character of this gate becomes manifest and
is verified through the presence of entanglement at the output for a product
two-mode coherent input state. By combining our controlled-phase gate with the
recently reported module for universal single-mode Gaussian operations [R. Ukai
et al., Phys. Rev. Lett. 106, 240504 (2011)], it is possible to implement
universal Gaussian operations on arbitrary multi-mode quantum optical states in
form of a fully measurement-based one-way quantum computation.Comment: 4 pages, 3 figure
Demonstration of unconditional one-way quantum computations for continuous variables
Quantum computing promises to exploit the laws of quantum mechanics for
processing information in ways fundamentally different from today's classical
computers, leading to unprecedented efficiency. One-way quantum computation,
sometimes referred to as the cluster model of quantum computation, is a very
promising approach to fulfil the capabilities of quantum information
processing. The cluster model is realizable through measurements on a highly
entangled cluster state with no need for controlled unitary evolutions. Here we
demonstrate unconditional one-way quantum computation experiments for
continuous variables using a linear cluster state of four entangled optical
modes. We implement an important set of quantum operations, linear
transformations, in the optical phase space through one-way computation. Though
not sufficient, these are necessary for universal quantum computation over
continuous variables, and in our scheme, in principle, any such linear
transformation can be unconditionally and deterministically applied to
arbitrary single-mode quantum states.Comment: 9 pages, 3 figure
Experimental realization of quantum teleportation as cluster computation
We demonstrate quantum teleportation of a coherent state as cluster computation using a four-mode linear cluster state. This is the first example of realization of cluster computation in continuous-variable systems