quantum physics

A Quantum-Enhanced Prototype Gravitational-Wave Detector

Matt Daniels — Fri, 29 Feb 2008 07:55:51 -0800

NOTE: This content was aggregated from RSS feed. Original source is http://arxiv.org/abs/0802.4118

The quantum nature of the electromagnetic field imposes a fundamental limit
on the sensitivity of optical precision measurements such as spectroscopy,
microscopy, and interferometry. The so-called quantum limit is set by the
zero-point fluctuations of the electromagnetic field, which constrain the
precision with which optical signals can be measured. In the world of precision
measurement, laser-interferometric gravitational wave (GW) detectors are the
most sensitive position meters ever operated, capable of measuring distance
changes on the order of 10^-18 m RMS over kilometer separations caused by GWs
from astronomical sources. The sensitivity of currently operational and future
GW detectors is limited by quantum optical noise. Here we demonstrate a 44%
improvement in displacement sensitivity of a prototype GW detector with
suspended quasi-free mirrors at frequencies where the sensitivity is
shot-noise-limited, by injection of a squeezed state of light. This
demonstration is a critical step toward implementation of squeezing-enhancement
in large-scale GW detectors.

(arXiv:0802.4118v1 [quant-ph])

Physics & Space Science

A Framework for Practical Quantum Cryptography

Matt Daniels — Fri, 29 Feb 2008 07:55:51 -0800

NOTE: This content was aggregated from RSS feed. Original source is http://arxiv.org/abs/0802.4155

Quantum information storage is becoming feasible...

Quantum cryptography is the first quantum information task to reach the level
of mature technology, already fit for commercialization. It aims at the
creation of a secret key between authorized partners connected by a quantum
channel and a classical authenticated channel, whence the proper name of
Quantum Key Distribution (QKD). The security of the key can in principle be
guaranteed without putting any restriction on the eavesdropper's power.

The first two sections provide a concise up-to-date review of QKD, biased
toward the practical side. The rest of the paper presents the essential
theoretical tools and the main experimental platforms (discrete variables,
continuous variables and distributed-phase-reference protocols) in a synthetic
framework, which highlights similarities and differences and is open to include
future progress.

(arXiv:0802.4155v1 [quant-ph])

Physics & Space Science

Revisiting the security of quantum dialogue and bidirectional quantum secure direct communication. (arXiv:0801.2420v2 [quant-ph]

Matt Daniels — Sun, 17 Feb 2008 19:20:12 -0800

NOTE: This content was aggregated from RSS feed. Original source is http://arxiv.org/abs/0801.2420

From the perspective of information theory and cryptography, we analyze the
security of two quantum dialogue protocols and a bidirectional quantum secure
direct communication (QSDC) protocol, and point out that the transmitted
information would be partly leaked out in them. That is, any eavesdropper can
elicit some information about the secrets from the public annunciations of the
legal users. This phenomenon should have been strictly forbidden in a quantum
secure communication. In fact, this problem exists in quite a few recent
proposals and, therefore, it deserves more research attention in the following
related study.

Physics & Space Science

Quantum information processing with single photons and atomic ensembles in microwave coplanar waveguide resonators

Matt Daniels — Sun, 17 Feb 2008 19:20:11 -0800

NOTE: This content was aggregated from RSS feed. Original source is http://arxiv.org/abs/0802.2154

We show that pairs of atoms optically excited to the Rydberg states can
strongly interact with each other via effective long-range dipole-dipole or van
der Waals interactions mediated by their non-resonant coupling to a common
microwave field mode of a superconducting coplanar waveguide cavity. These
cavity mediated interactions can be employed to generate single photons and to
realize in a scalable configuration a universal phase gate between pairs of
single photon pulses propagating or stored in atomic ensembles in the regime of
electromagnetically induced transparency.

Signals Round 3

Teleportation using continuous variable quantum cloning machine. (arXiv:0802.2156v1)

Matt Daniels — Sun, 17 Feb 2008 19:20:11 -0800

NOTE: This content was aggregated from RSS feed. Original source is http://arxiv.org/abs/0802.2156

We show that an unknown quantum state in phase space can be teleported via
three-mode entanglement generated by continuous variable quantum cloning
machine (transformation). Further, proceeding with our teleportation protocol
we are able to improve the fidelity of teleportation obtained by Loock et.al.
[Phys.Rev.Lett. 84, 3482(2000)]. Also we study here the entanglement between
the two output copies from cloning machine.

Signals Round 3

Quantum Chemistry for Pollution Abatement

Alex Soojung-Kim Pang — Tue, 23 Oct 2007 11:10:30 -0700

Description

Nanomanipulation at the quantum level of chemical reactions could ameliorate chemical pollution.

Nitrogen and phosphorus from agricultural runoff, among other sources, have created large zones of eutrophication and hypoxia, essentially dead zones, in the oceans. Smokestack emissions from industry have likewise damaged the atmosphere. New technologies could emerge from quantum manipulation of chemical reactions to ameliorate these conditions. The more precise our understanding of basic chemical reactions, the more we will be able to control unintended consequences and ameliorate pollutant impacts on the environment.

This will be enabled by:

Progress in fundamental understanding of quantum chemistry

Early indicators include:

Current research by Paul Blowers at the University of Arizona using the supercomputer at the US National Center for Supercomputing Applications (NCSA) to model quantum chemical reactions in powerplant smokestacks in the interests of ameliorating chemical pollution

What to watch:

Advances in supercomputing further our understanding of basic chemical reactions.
Commercial 'green' products begin emerging from quantum chemistry.