28 research outputs found
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
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
Violation of Bells inequality using continuous variable measurements
A Bell inequality is a fundamental test to rule out local hidden variable
model descriptions of correlations between two physically separated systems.
There have been a number of experiments in which a Bell inequality has been
violated using discrete-variable systems. We demonstrate a violation of Bells
inequality using continuous variable quadrature measurements. By creating a
four-mode entangled state with homodyne detection, we recorded a clear
violation with a Bell value of . This opens new
possibilities for using continuous variable states for device independent
quantum protocols.Comment: 5 pages, 4 figures, lette
Experimental demonstration of Gaussian protocols for one-sided device-independent quantum key distribution
Nonlocal correlations, a longstanding foundational topic in quantum
information, have recently found application as a resource for cryptographic
tasks where not all devices are trusted, for example in settings with a highly
secure central hub, such as a bank or government department, and less secure
satellite stations which are inherently more vulnerable to hardware "hacking"
attacks. The asymmetric phenomena of Einstein-Podolsky-Rosen steering plays a
key role in one-sided device-independent quantum key distribution (1sDI-QKD)
protocols. In the context of continuous-variable (CV) QKD schemes utilizing
Gaussian states and measurements, we identify all protocols that can be 1sDI
and their maximum loss tolerance. Surprisingly, this includes a protocol that
uses only coherent states. We also establish a direct link between the relevant
EPR steering inequality and the secret key rate, further strengthening the
relationship between these asymmetric notions of nonlocality and device
independence. We experimentally implement both entanglement-based and
coherent-state protocols, and measure the correlations necessary for 1sDI key
distribution up to an applied loss equivalent to 7.5 km and 3.5 km of optical
fiber transmission respectively. We also engage in detailed modelling to
understand the limits of our current experiment and the potential for further
improvements. The new protocols we uncover apply the cheap and efficient
hardware of CVQKD systems in a significantly more secure setting.Comment: Addition of experimental results and (several) new author
Optimal Location of Two Laser-interferometric Detectors for Gravitational Wave Backgrounds at 100 MHz
Recently, observational searches for gravitational wave background (GWB) have
been developed and given constraints on the energy density of GWB in a broad
range of frequencies. These constraints have already resulted in the rejection
of some theoretical models of relatively large GWB spectra. However, at 100
MHz, there is no strict upper limit from direct observation, though an indirect
limit exists due to He4 abundance due to big-bang nucleosynthesis. In our
previous paper, we investigated the detector designs that can effectively
respond to GW at high frequencies, where the wavelength of GW is comparable to
the size of a detector, and found that the configuration, a so-called
synchronous-recycling interferometer is best at these sensitivity. In this
paper, we investigated the optimal location of two synchronous-recycling
interferometers and derived their cross-correlation sensitivity to GWB. We
found that the sensitivity is nearly optimized and hardly changed if two
coaligned detectors are located within a range 0.2 m, and that the sensitivity
achievable in an experiment is far below compared with the constraint
previously obtained in experiments.Comment: 17 pages, 6 figure
Theory and Applications of Non-Relativistic and Relativistic Turbulent Reconnection
Realistic astrophysical environments are turbulent due to the extremely high
Reynolds numbers. Therefore, the theories of reconnection intended for
describing astrophysical reconnection should not ignore the effects of
turbulence on magnetic reconnection. Turbulence is known to change the nature
of many physical processes dramatically and in this review we claim that
magnetic reconnection is not an exception. We stress that not only
astrophysical turbulence is ubiquitous, but also magnetic reconnection itself
induces turbulence. Thus turbulence must be accounted for in any realistic
astrophysical reconnection setup. We argue that due to the similarities of MHD
turbulence in relativistic and non-relativistic cases the theory of magnetic
reconnection developed for the non-relativistic case can be extended to the
relativistic case and we provide numerical simulations that support this
conjecture. We also provide quantitative comparisons of the theoretical
predictions and results of numerical experiments, including the situations when
turbulent reconnection is self-driven, i.e. the turbulence in the system is
generated by the reconnection process itself. We show how turbulent
reconnection entails the violation of magnetic flux freezing, the conclusion
that has really far reaching consequences for many realistically turbulent
astrophysical environments. In addition, we consider observational testing of
turbulent reconnection as well as numerous implications of the theory. The
former includes the Sun and solar wind reconnection, while the latter include
the process of reconnection diffusion induced by turbulent reconnection, the
acceleration of energetic particles, bursts of turbulent reconnection related
to black hole sources as well as gamma ray bursts. Finally, we explain why
turbulent reconnection cannot be explained by turbulent resistivity or derived
through the mean field approach.Comment: 66 pages, 24 figures, a chapter of the book "Magnetic Reconnection -
Concepts and Applications", editors W. Gonzalez, E. N. Parke
The Hyper Suprime-Cam SSP survey: Overview and survey design
Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2-m Subaru telescope on the summit of Mauna Kea in Hawaii. A team of scientists from Japan, Taiwan, and Princeton University is using HSC to carry out a 300-night multi-band imaging survey of the high-latitude sky. The survey includes three layers: the Wide layer will cover 1400 deg2 in five broad bands (grizy), with a 5 σ point-source depth of r ≈ 26. The Deep layer covers a total of 26 deg2 in four fields, going roughly a magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter still in two pointings of HSC (a total of 3.5 deg2). Here we describe the instrument, the science goals of the survey, and the survey strategy and data processing. This paper serves as an introduction to a special issue of the Publications of the Astronomical Society of Japan, which includes a large number of technical and scientific papers describing results from the early phases of this survey