1,810 research outputs found
The Quantum State of an Ideal Propagating Laser Field
We give a quantum information-theoretic description of an ideal propagating
CW laser field and reinterpret typical quantum-optical experiments in light of
this. In particular we show that contrary to recent claims [T. Rudolph and B.
C. Sanders, Phys. Rev. Lett. 87, 077903 (2001)], a conventional laser can be
used for quantum teleportation with continuous variables and for generating
continuous-variable entanglement. Optical coherence is not required, but phase
coherence is. We also show that coherent states play a priveleged role in the
description of laser light.Comment: 4 pages RevTeX, to appear in PRL. For an extended version see
quant-ph/011115
One Loop Renormalization of the Littlest Higgs Model
In Little Higgs models a collective symmetry prevents the Higgs from
acquiring a quadratically divergent mass at one loop. This collective symmetry
is broken by weakly gauged interactions. Terms, like Yukawa couplings, that
display collective symmetry in the bare Lagrangian are generically renormalized
into a sum of terms that do not respect the collective symmetry except possibly
at one renormalization point where the couplings are related so that the
symmetry is restored. We study here the one loop renormalization of a
prototypical example, the Littlest Higgs Model. Some features of the
renormalization of this model are novel, unfamiliar form similar chiral
Lagrangian studies.Comment: 23 pages, 17 eps figure
Trust in Peer-to-Peer content distribution protocols
Abstract. The distribution of virtual goods like multimedia data relies on the trustworthiness of the distribution system. Recent concepts for the distribution based on peer to peer networks like BitTorrent require new approaches to establish the needed level of trust in the overall functionality of the system. This paper explores the integration of hardware based trust concepts from the domain of Trusted Computing in the well know BitTorrent protocol suite
Degradation of a quantum directional reference frame as a random walk
We investigate if the degradation of a quantum directional reference frame
through repeated use can be modeled as a classical direction undergoing a
random walk on a sphere. We demonstrate that the behaviour of the fidelity for
a degrading quantum directional reference frame, defined as the average
probability of correctly determining the orientation of a test system, can be
fit precisely using such a model. Physically, the mechanism for the random walk
is the uncontrollable back-action on the reference frame due to its use in a
measurement of the direction of another system. However, we find that the
magnitude of the step size of this random walk is not given by our classical
model and must be determined from the full quantum description.Comment: 5 pages, no figures. Comments are welcome. v2: several changes to
clarify the key results. v3: journal reference added, acknowledgements and
references update
Defending Continuous Variable Teleportation: Why a laser is a clock, not a quantum channel
It has been argued [T. Rudolph and B.C. Sanders, Phys. Rev. Lett. {\bf 87},
077903 (2001)] that continuous-variable quantum teleportation at optical
frequencies has not been achieved because the source used (a laser) was not
`truly coherent'. Van Enk, and Fuchs [Phys. Rev. Lett, {\bf 88}, 027902
(2002)], while arguing against Rudolph and Sanders, also accept that an
`absolute phase' is achievable, even if it has not been achieved yet. I will
argue to the contrary that `true coherence' or `absolute phase' is always
illusory, as the concept of absolute time (at least for frequencies beyond
direct human experience) is meaningless. All we can ever do is to use an agreed
time standard. In this context, a laser beam is fundamentally as good a `clock'
as any other. I explain in detail why this claim is true, and defend my
argument against various objections. In the process I discuss super-selection
rules, quantum channels, and the ultimate limits to the performance of a laser
as a clock. For this last topic I use some earlier work by myself [Phys. Rev. A
{\bf 60}, 4083 (1999)] and Berry and myself [Phys. Rev. A {\bf 65}, 043803
(2002)] to show that a Heisenberg-limited laser with a mean photon number
can synchronize independent clocks each with a mean-square error of
radians.Comment: 22 pages, to be published in a special issue of J. Opt. B. This is an
extended version of quant-ph/0303116 (the SPIE conference paper
Separability and entanglement in 2x3xN composite quantum systems
The separability and entanglement of quantum mixed states in \Cb^2 \otimes
\Cb^3 \otimes \Cb^N composite quantum systems are investigated. It is shown
that all quantum states with positive partial transposes and rank
are separable.Comment: Latex, 15 page
Ion beam lithography for Fresnel zone plates in X-ray microscopy
Fresnel Zone Plates (FZP) are to date very successful focusing optics for
X-rays. Established methods of fabrication are rather complex and based on
electron beam lithography (EBL). Here, we show that ion beam lithography (IBL)
may advantageously simplify their preparation. A FZP operable from the extreme
UV to the limit of the hard X-ray was prepared and tested from 450 eV to 1500
eV. The trapezoidal profile of the FZP favorably activates its 2nd order focus.
The FZP with an outermost zone width of 100 nm allows the visualization of
features down to 61, 31 and 21 nm in the 1st, 2nd and 3rd order focus
respectively. Measured efficiencies in the 1st and 2nd order of diffraction
reach the theoretical predictions
Quantum Physics from A to Z
This is a collection of statements gathered on the occasion of the Quantum
Physics of Nature meeting in Vienna.Comment: 3 pages, Quantum Physics of Nature (QUPON) Conference, Vienna,
Austria, May 22nd-26th, 2005; v4: more contribution
- …