556 research outputs found
Model of Thermal Wavefront Distortion in Interferometric Gravitational-Wave Detectors I: Thermal Focusing
We develop a steady-state analytical and numerical model of the optical
response of power-recycled Fabry-Perot Michelson laser gravitational-wave
detectors to thermal focusing in optical substrates. We assume that the thermal
distortions are small enough that we can represent the unperturbed intracavity
field anywhere in the detector as a linear combination of basis functions
related to the eigenmodes of one of the Fabry-Perot arm cavities, and we take
great care to preserve numerically the nearly ideal longitudinal phase
resonance conditions that would otherwise be provided by an external
servo-locking control system. We have included the effects of nonlinear thermal
focusing due to power absorption in both the substrates and coatings of the
mirrors and beamsplitter, the effects of a finite mismatch between the
curvatures of the laser wavefront and the mirror surface, and the diffraction
by the mirror aperture at each instance of reflection and transmission. We
demonstrate a detailed numerical example of this model using the MATLAB program
Melody for the initial LIGO detector in the Hermite-Gauss basis, and compare
the resulting computations of intracavity fields in two special cases with
those of a fast Fourier transform field propagation model. Additional
systematic perturbations (e.g., mirror tilt, thermoelastic surface
deformations, and other optical imperfections) can be included easily by
incorporating the appropriate operators into the transfer matrices describing
reflection and transmission for the mirrors and beamsplitter.Comment: 24 pages, 22 figures. Submitted to JOSA
Properties of implanted and CVD incorporated nitrogen-vacancy centers: preferential charge state and preferential orientation
The combination of the long electron state spin coherence time and the optical coupling of the ground electronic states to an excited state manifold makes the nitrogen-vacancy (NV) center in diamond an attractive candidate for quantum information processing. To date the best spin and optical properties have been found in centers deep within the diamond crystal. For useful devices it will be necessary to engineer NVs with similar properties close to the diamond surface. We report on properties including charge state control and preferential orientation for near surface NVs formed either in CVD growth or through implantation and annealing
Secure self-calibrating quantum random bit generator
Random bit generators (RBGs) are key components of a variety of information
processing applications ranging from simulations to cryptography. In
particular, cryptographic systems require "strong" RBGs that produce
high-entropy bit sequences, but traditional software pseudo-RBGs have very low
entropy content and therefore are relatively weak for cryptography. Hardware
RBGs yield entropy from chaotic or quantum physical systems and therefore are
expected to exhibit high entropy, but in current implementations their exact
entropy content is unknown. Here we report a quantum random bit generator
(QRBG) that harvests entropy by measuring single-photon and entangled
two-photon polarization states. We introduce and implement a quantum
tomographic method to measure a lower bound on the "min-entropy" of the system,
and we employ this value to distill a truly random bit sequence. This approach
is secure: even if an attacker takes control of the source of optical states, a
secure random sequence can be distilled.Comment: 5 pages, 2 figure
Production of oriented nitrogen-vacancy color centers in synthetic diamond
The negatively charged nitrogen-vacancy (NV-) center in diamond is an
attractive candidate for applications that range from magnetometry to quantum
information processing. Here we show that only a fraction of the nitrogen
(typically < 0.5 %) incorporated during homoepitaxial diamond growth by
Chemical Vapor Deposition (CVD) is in the form of undecorated NV- centers.
Furthermore, studies on CVD diamond grown on (110) oriented substrates show a
near 100% preferential orientation of NV- centers along only the [111] and
[-1-11] directions, rather than the four possible orientations. The results
indicate that NV centers grow in as units, as the diamond is deposited, rather
than by migration and association of their components. The NV unit of the NVH-
is similarly preferentially oriented, but it is not possible to determine
whether this defect was formed by H capture at a preferentially aligned NV
center or as a complete unit. Reducing the number of NV orientations from 4
orientations to 2 orientations should lead to increased optically-detected
magnetic resonance contrast and thus improved magnetic sensitivity in
ensemble-based magnetometry.Comment: 13 Pages (inlcuding suplementary information), 4 figure
Observation of the dynamic Jahn-Teller effect in the excited states of nitrogen-vacancy centers in diamond
The optical transition linewidth and emission polarization of single
nitrogen-vacancy (NV) centers are measured from 5 K to room temperature.
Inter-excited state population relaxation is shown to broaden the zero-phonon
line and both the relaxation and linewidth are found to follow a T^5 dependence
for T up to 100 K. This dependence indicates that the dynamic Jahn-Teller
effect is the dominant dephasing mechanism for the NV optical transitions at
low temperatures
Low-temperature tapered-fiber probing of diamond NV ensembles coupled to GaP microcavities
In this work we present a platform for testing the device performance of a
cavity-emitter system, using an ensemble of emitters and a tapered optical
fiber. This method provides high-contrast spectra of the cavity modes,
selective detection of emitters coupled to the cavity, and an estimate of the
device performance in the single- emitter case. Using nitrogen-vacancy (NV)
centers in diamond and a GaP optical microcavity, we are able to tune the
cavity onto the NV resonance at 10 K, couple the cavity-coupled emission to a
tapered fiber, and measure the fiber-coupled NV spontaneous emission decay.
Theoretically we show that the fiber-coupled average Purcell factor is 2-3
times greater than that of free-space collection; although due to ensemble
averaging it is still a factor of 3 less than the Purcell factor of a single,
ideally placed center.Comment: 15 pages, 6 figure
A symmetry analyser for non-destructive Bell state detection using EIT
We describe a method to project photonic two-qubit states onto the symmetric
and antisymmetric subspaces of their Hilbert space. This device utilizes an
ancillary coherent state, together with a weak cross-Kerr non-linearity,
generated, for example, by electromagnetically induced transparency. The
symmetry analyzer is non-destructive, and works for small values of the
cross-Kerr coupling. Furthermore, this device can be used to construct a
non-destructive Bell state detector.Comment: Final published for
Database Search Strategies for Proteomic Data Sets Generated by Electron Capture Dissociation Mass Spectrometry
Large data sets of electron capture dissociation (ECD) mass spectra from proteomic experiments are rich in information; however, extracting that information in an optimal manner is not straightforward. Protein database search engines currently available are designed for low resolution CID data, from which Fourier transform ion cyclotron resonance (FT-ICR) ECD data differs significantly. ECD mass spectra contain both z-prime and z-dot fragment ions (and c-prime and c-dot); ECD mass spectra contain abundant peaks derived from neutral losses from charge-reduced precursor ions; FT-ICR ECD spectra are acquired with a larger precursor m/z isolation window than their low-resolution CID counterparts. Here, we consider three distinct stages of postacquisition analysis: (1) processing of ECD mass spectra prior to the database search; (2) the database search step itself and (3) postsearch processing of results. We demonstrate that each of these steps has an effect on the number of peptides identified, with the postsearch processing of results having the largest effect. We compare two commonly used search engines: Mascot and OMSSA. Using an ECD data set of modest size (3341 mass spectra) from a complex sample (mouse whole cell lysate), we demonstrate that search results can be improved from 630 identifications (19% identification success rate) to 1643 identifications (49% identification success rate). We focus in particular on improving identification rates for doubly charged precursors, which are typically low for ECD fragmentation. We compare our presearch processing algorithm with a similar algorithm recently developed for electron transfer dissociation (ETD) data
Applications of Coherent Population Transfer to Quantum Information Processing
We develop a theoretical framework for the exploration of quantum mechanical
coherent population transfer phenomena, with the ultimate goal of constructing
faithful models of devices for classical and quantum information processing
applications. We begin by outlining a general formalism for weak-field quantum
optics in the Schr\"{o}dinger picture, and we include a general
phenomenological representation of Lindblad decoherence mechanisms. We use this
formalism to describe the interaction of a single stationary multilevel atom
with one or more propagating classical or quantum laser fields, and we describe
in detail several manifestations and applications of electromagnetically
induced transparency. In addition to providing a clear description of the
nonlinear optical characteristics of electromagnetically transparent systems
that lead to ``ultraslow light,'' we verify that -- in principle -- a
multi-particle atomic or molecular system could be used as either a low power
optical switch or a quantum phase shifter. However, we demonstrate that the
presence of significant dephasing effects destroys the induced transparency,
and that increasing the number of particles weakly interacting with the probe
field only reduces the nonlinearity further. Finally, a detailed calculation of
the relative quantum phase induced by a system of atoms on a superposition of
spatially distinct Fock states predicts that a significant quasi-Kerr
nonlinearity and a low entropy cannot be simultaneously achieved in the
presence of arbitrary spontaneous emission rates. Within our model, we identify
the constraints that need to be met for this system to act as a one-qubit and a
two-qubit conditional phase gate.Comment: 25 pages, 14 figure
Weak nonlinearities: A new route to optical quantum computation
Quantum information processing (QIP) offers the promise of being able to do
things that we cannot do with conventional technology. Here we present a new
route for distributed optical QIP, based on generalized quantum non-demolition
measurements, providing a unified approach for quantum communication and
computing. Interactions between photons are generated using weak
non-linearities and intense laser fields--the use of such fields provides for
robust distribution of quantum information. Our approach requires only a
practical set of resources, and it uses these very efficiently. Thus it
promises to be extremely useful for the first quantum technologies, based on
scarce resources. Furthermore, in the longer term this approach provides both
options and scalability for efficient many-qubit QIP.Comment: 7 Pages, 4 Figure
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