960 research outputs found
Avoiding the uncertainty from correlation between |Delta m_{31}^2| and CP phase delta in nu_mu --> nu_mu long baseline experiments
We introduce a new index I_{Delta m_{31}^2} to find where is the better setup
of the baseline length and energy to avoid as well as possible the uncertainty
from the correlation between Delta m_{31}^2 and cos(delta) in nu_mu --> nu_mu
long baseline experiments.Comment: 6 pages, 9 figure
Purification of photon subtraction from continuous squeezed light by filtering
Photon subtraction from squeezed states is a powerful scheme to create good
approximation of so-called Schr\"odinger cat states. However, conventional
continuous-wave-based methods actually involve some impurity in squeezing of
localized wavepackets, even in the ideal case of no optical losses. Here we
theoretically discuss this impurity, by introducing mode-match of squeezing.
Furthermore, here we propose a method to remove this impurity by filtering the
photon-subtraction field. Our method in principle enables creation of pure
photon-subtracted squeezed states, which was not possible with conventional
methods.Comment: 10 pages, 6 figure
Demonstration of a universal one-way quantum quadratic phase gate
We demonstrate a quadratic phase gate for one-way quantum computation in the
continuous-variable regime. This canonical gate, together with phase-space
displacements and Fourier rotations, completes the set of universal gates for
realizing any single-mode Gaussian transformation such as arbitrary squeezing.
As opposed to previous implementations of measurement-based squeezers, the
current gate is fully controlled by the local oscillator phase of the homodyne
detector. Verifying this controllability, we give an experimental demonstration
of the principles of one-way quantum computation over continuous variables.
Moreover, we can observe sub-shot-noise quadrature variances in the output
states, confirming that nonclassical states are created through cluster
computation.Comment: 5 pages, 4 figure
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
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
Creation, storage, and on-demand release of optical quantum states with a negative Wigner function
Highly nonclassical quantum states of light, characterized by Wigner
functions with negative values, have been created so far only in a heralded
fashion. In this case, the desired output emerges rarely and randomly from a
quantum-state generator. An important example is the heralded production of
high-purity single-photon states, typically based on some nonlinear optical
interaction. In contrast, on-demand single-photon sources were also reported,
exploiting the quantized level structure of matter systems. These sources,
however, lead to highly impure output states, composed mostly of vacuum. While
such impure states may still exhibit certain single-photon-like features such
as anti-bunching, they are not enough nonclassical for advanced quantum
information processing. On the other hand, the intrinsic randomness of pure,
heralded states can be circumvented by first storing and then releasing them on
demand. Here we propose such a controlled release, and we experimentally
demonstrate it for heralded single photons. We employ two optical cavities,
where the photons are both created and stored inside one cavity, and finally
released through a dynamical tuning of the other cavity. We demonstrate storage
times of up to 300 ns, while keeping the single-photon purity around 50% after
storage. This is the first demonstration of a negative Wigner function at the
output of an on-demand photon source or a quantum memory. In principle, our
storage system is compatible with all kinds of nonclassical states, including
those known to be essential for many advanced quantum information protocols.Comment: 14 pages, 5 figure
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