2,284 research outputs found
A model independent approach towards resource count and precision limits in a general measurement
A formulation towards quantifying resource count used in a measurement, that
is independent of the model of the measurement dynamics(Quantum/Classical), is
considered. For any general measurement with discrete outcomes, it is
found that there is a unique probability distribution that minimizes the
measurement error, with the error scaling as . For a measurement with a
finite resource, this absolute bound implies the resource count to be
equal to the possible outcomes i.e. . This formulation therefore provides
a model independent route towards estimating resource count used in any general
measurement scheme.Comment: 4+1 pages and supplementary informatio
Nonlinear, anisotropic and giant photoconductivity in intrinsic and doped graphene
We present a framework to calculate the anisotropic and non-linear
photoconductivity for two band systems with application to graphene. In
contrast to the usual perturbative (second order in the optical field strength)
techniques, we calculate photoconductivity to all orders in the optical field
strength. In particular, for graphene, we find the photoresponse to be giant
(at large optical field strengths) and anisotropic. The anisotropic
photoresponse in graphene is correlated with polarization of the incident
field, with the response being similar to that of a half-wave plate. We predict
that the anisotropy in the simultaneous measurement of longitudinal
() and transverse photoconductivity, with four
probes, offers a unique experimental signature of the photo-voltaic response,
distinguishing it from the thermal-Seebeck and bolometric effects in
photoresponse.Comment: 5 pages, 4 figures. Comments and feedback are invite
Terahertz modulated optical sideband generation in graphene
Exploration of optical non-linear response of graphene predominantly relies
on ultra-short time domain measurements. Here we propose an alternate technique
that uses frequency modulated continuous wavefront optical fields, thereby
probing graphene's steady state non-linear response. We predict frequency
sideband generation in the reflected field that originates from coherent
electron dynamics of the photo-excited carriers. The corresponding threshold in
input intensity for optimal sideband generation provides a direct measure of
the third order optical non-linearity in graphene. Our formulation yields
analytic forms for the generated sideband intensity, is applicable to generic
two-band systems and suggests a range of applications that include switching of
frequency sidebands using non-linear phase shifts and generation of frequency
combs.Comment: To appear in Phys. Rev.
Decay dynamics in a strongly driven atom-molecule coupled system
Within the framework of master equation, we study decay dynamics of an
atom-molecule system strongly coupled by two photoassociation lasers. Summing
over the infinite number of electromagnetic vacuum modes that are coupled to
the laser-dressed atom-molecule system, we obtain an integro-differential
master equation for the the system's reduced density matrix. The equation is
numerically solved to describe system dynamics in the presence of decay. In
particular, we discuss correlated spontaneous emission from a pair of
electronically excited diatomic ro-vibrational states due to their laser
induced coupling to the ground continuum of atomic scattering states. This
allows us to calculate time-dependence of emitted radiation intensity. It
exhibits quantum beats due to coherent dynamics. The phase difference between
the two driving fields is found to significantly affect the decay dynamics and
the beats. Our results demonstrate the possibility to control decay from the
molecular excited states and the decoherence between them by changing the
relative intensity and the phase between the lasers. We further show that, if
the ground-state continuum has a shape resonance at a low energy, then the
quantum beats show two distinctive time scales of oscillations in the strong
coupling regime. One of the time scales originates from the energy gap between
the two excited states while the other time scale corresponds to the collision
energy at which free-bound Franck-Condon overlap is resonantly peaked due to
the shape resonance.Comment: 23 pages, 10 figures, accepted in J. Phys. B: At. Mol. Opt. Phy
A comparative study of performance of fpga based mel filter bank & bark filter bank
The sensitivity of human ear is dependent on frequency which is nonlinearly
resolved across the audio spectrum .Now to improve the recognition performance
in a similar non linear approach requires a front -end design, suggested by
empirical evidences. A popular alternative to linear prediction based analysis
is therefore filter bank analysis since this provides a much more
straightforward route to obtain the desired non-linear frequency resolution.
MEL filter bank and BARK filter bank are two popular filter bank analysis
techniques. This paper presents FPGA based implementation of MEL filter bank
and BARK filter bank with different bandwidths and different signal spectrum
ranges. The designs have been implemented using VHDL, simulated and verified
using Xilinx 11.1.For each filter bank, the basic building block is implemented
in Spartan 3E. A comparative study among these two mentioned filter banks is
also done in this paper.Comment: 16 pages, 20 figures, 6 tables; International Journal of Artificial
Intelligence & Applications (IJAIA), Vol.3, No.3, May 201
Simplified measurement of the Bell parameter within quantum mechanics
We point out that, if one accepts the validity of quantum mechanics, the Bell
parameter for the polarization state of two photons can be measured in a
simpler way than by the standard procedure [Clauser, Horne, Shimony, and Holt,
Phys. Rev. Lett. 23, 880 (1969)]. The proposed method requires only two
measurements with parallel linear-polarizer settings for Alice and Bob at 0 and
45 degrees, and yields a significantly smaller statistical error for a large
Bell parameter.Comment: 4 pages, 1 figure. Submitted to Physical Review
A controllable single photon beam-splitter as a node of a quantum network
A model for a controlled single-photon beam-splitter is proposed and
analysed. It consists of two crossed optical-cavities with overlapping waists,
dynamically coupled to a single flying atom. The system is shown to route a
single photon with near-unity efficiency in an effective "weak-coupling"
regime. Furthermore, two such nodes, forming a segment of a quantum network,
are shown to perform several controlled quantum operations. All one-qubit
operations involve a transfer of a photon from one cavity to another in a
single node, while two-qubit operations involve transfer from one node to a
next one, coupled via an optical fiber. Novel timing protocols for classical
optical fields are found to simplify possible experimental realizations along
with achievable effective parameter regime. Though our analysis here is
restricted to a cavity-QED scenario, basic features of the model can be
extended to various other physical systems including gated quantum dots,
circuit-QED or opto-mechanical elements.Comment: 24 pages, 7 figure
Quantum counterpart of Measure synchronization: A study on a pair of Harper systems
Measure synchronization is a well-known phenomenon in coupled classical
Hamiltonian systems over last two decades. In this paper, synchronization for
coupled Harper system is investigated in both classical and quantum contexts.
The concept of measure synchronization involves with the phase space and it
seems that the measure synchronization is restricted in classical limit. But,
on the contrary, here, we have extended the aforesaid synchronization in
quantum domain. In quantum context, the coupling occurs between two many body
systems via a time and site dependent potential. The coupling leads to the
generation of entanglement between the quantum systems. We have used a
technique, which is already accepted in the classical domain, in both the
contexts to establish a connection between classical and quantum scenarios.
Interestingly, results corresponding to both the cases lead to some common
features.Comment: 13 pages, 9 figure
Quantum enhanced precision in a collective measurement
We explore the role of on precision in
estimation of a single parameter. Collective measurements are represented by
observables which commute with all permutations of the probe particles. We show
that with this constraint, quantum bits(qubits) outperform classical
bits(non-superposable bits) in optimizing precision. Specifically, we prove
that while precision in a collective measurement is loosely bounded by
for classical bits, using qubits it is tightly
bounded by . This bound is consistent with quantum
metrology protocols with the collective measurement requiring an entangled
probe state to saturate. Finally, we construct a canonical measurement protocol
that saturates this bound.Comment: 16 Pages, 1 Figure, 2 Table
Nonlinear optical conductivity of a generic two band systems, with application to doped and gapped graphene
We present a general formulation to calculate the dynamic optical
conductivity, beyond the linear response regime, of any electronic system whose
quasiparticle dispersion is described by a two band model. Our phenomenological
model is based on the optical Bloch equations. In the steady state regime it
yields an analytic solution for the population inversion and the interband
coherence, which are nonlinear in the optical field intensity, including finite
doping and temperature effects. We explicitly show that the optical
nonlinearities are controlled by a single dimensionless parameter which is
directly proportional to the incident field strength and inversely proportional
to the optical frequency. This identification leads to a unified way to study
the dynamical conductivity and the differential transmission spectrum across a
wide range of optical frequencies, and optical field strength. We use our
formalism to analytically calculate the nonlinear optical conductivity of doped
and gapped graphene, deriving the well known universal ac conductivity of
in the linear response regime of low optical
intensities (or equivalently high frequencies) and non-linear deviations from
it which appear at high laser intensities (or low frequencies) including the
impact of finite doping and band-gap opening.Comment: 12 pages, 6 figures; Criticism/Comments are welcom
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