8,906 research outputs found
Environment Assisted Metrology with Spin Qubit
We investigate the sensitivity of a recently proposed method for precision
measurement [Phys. Rev. Lett. 106, 140502 (2011)], focusing on an
implementation based on solid-state spin systems. The scheme amplifies a
quantum sensor response to weak external fields by exploiting its coupling to
spin impurities in the environment. We analyze the limits to the sensitivity
due to decoherence and propose dynamical decoupling schemes to increase the
spin coherence time. The sensitivity is also limited by the environment spin
polarization; therefore we discuss strategies to polarize the environment spins
and present a method to extend the scheme to the case of zero polarization. The
coherence time and polarization determine a figure of merit for the
environment's ability to enhance the sensitivity compared to echo-based sensing
schemes. This figure of merit can be used to engineer optimized samples for
high-sensitivity nanoscale magnetic sensing, such as diamond nanocrystals with
controlled impurity density.Comment: 9 pages, 6 figure
Environment Assisted Precision Measurement
We describe a method to enhance the sensitivity of precision measurements
that takes advantage of a quantum sensor's environment to amplify its response
to weak external perturbations. An individual qubit is used to sense the
dynamics of surrounding ancillary qubits, which are in turn affected by the
external field to be measured. The resulting sensitivity enhancement is
determined by the number of ancillas that are coupled strongly to the sensor
qubit; it does not depend on the exact values of the coupling strengths and is
resilient to many forms of decoherence. The method achieves nearly
Heisenberg-limited precision measurement, using a novel class of entangled
states. We discuss specific applications to improve clock sensitivity using
trapped ions and magnetic sensing based on electronic spins in diamond.Comment: 4 pages, 3 figure
A Group-Based Yule Model for Bipartite Author-Paper Networks
This paper presents a novel model for author-paper networks, which is based
on the assumption that authors are organized into groups and that, for each
research topic, the number of papers published by a group is based on a
success-breeds-success model. Collaboration between groups is modeled as random
invitations from a group to an outside member. To analyze the model, a number
of different metrics that can be obtained in author-paper networks were
extracted. A simulation example shows that this model can effectively mimic the
behavior of a real-world author-paper network, extracted from a collection of
900 journal papers in the field of complex networks.Comment: 13 pages (preprint format), 7 figure
Stability of adhesion clusters under constant force
We solve the stochastic equations for a cluster of parallel bonds with shared
constant loading, rebinding and the completely dissociated state as an
absorbing boundary. In the small force regime, cluster lifetime grows only
logarithmically with bond number for weak rebinding, but exponentially for
strong rebinding. Therefore rebinding is essential to ensure physiological
lifetimes. The number of bonds decays exponentially with time for most cases,
but in the intermediate force regime, a small increase in loading can lead to
much faster decay. This effect might be used by cell-matrix adhesions to induce
signaling events through cytoskeletal loading.Comment: Revtex, 4 pages, 4 Postscript files include
Comparison of work fluctuation relations
We compare two predictions regarding the microscopic fluctuations of a system
that is driven away from equilibrium: one due to Crooks [J. Stat. Phys. 90,
1481 (1998)] which has gained recent attention in the context of nonequilibrium
work and fluctuation theorems, and an earlier, analogous result obtained by
Bochkov and Kuzovlev [Zh. Eksp. Teor. Fiz. 72(1), 238247 (1977)]. Both results
quantify irreversible behavior by comparing probabilities of observing
particular microscopic trajectories during thermodynamic processes related by
time-reversal, and both are expressed in terms of the work performed when
driving the system away from equilibrium. By deriving these two predictions
within a single, Hamiltonian framework, we clarify the precise relationship
between them, and discuss how the different definitions of work used by the two
sets of authors gives rise to different physical interpretations. We then
obtain a extended fluctuation relation that contains both the Crooks and the
Bochkov-Kuzovlev results as special cases.Comment: 14 pages with 1 figure, accepted for publication in the Journal of
Statistical Mechanic
Variational and Potential Formulation for Stochastic Partial Differential Equations
There is recent interest in finding a potential formulation for Stochastic
Partial Differential Equations (SPDEs). The rationale behind this idea lies in
obtaining all the dynamical information of the system under study from one
single expression. In this Letter we formally provide a general Lagrangian
formalism for SPDEs using the Hojman et al. method. We show that it is possible
to write the corresponding effective potential starting from an s-equivalent
Lagrangean, and that this potential is able to reproduce all the dynamics of
the system, once a special differential operator has been applied. This
procedure can be used to study the complete time evolution and spatial
inhomogeneities of the system under consideration, and is also suitable for the
statistical mechanics description of the problem. Keywords: stochastic partial
differential equations, variational formulation, effective potential. PACS:
45.20.Jj; 02.50.-r; 02.50.Ey.Comment: Letter, 4 pages, no figures; v2: references added, minor change
Two-atom dark states in electromagnetic cavities
The center-of-mass motion of two two-level atoms coupled to a single damped
mode of an electromagnetic resonator is investigated. For the case of one atom
being initially excited and the cavity mode in the vacuum state it is shown
that the atomic time evolution is dominated by the appearance of dark states.
These states, in which the initial excitation is stored in the internal atomic
degrees of freedom and the atoms become quantum mechanically entangled, are
almost immune against photon loss from the cavity. Various properties of the
dark states within and beyond the Raman-Nath approximation of atom optics are
worked out.Comment: 8 pages, 4 figure
A general condition of inflationary cosmology on trans-Planckian physics
We consider a more general initial condition satisfying the minimal
uncertainty relationship. We calculate the power spectrum of a simple model in
inflationary cosmology. The results depend on perturbations generated below a
fundamental scale, e.g. the Planck scale.Comment: 7 pages, References adde
Microwave quantum optics and electron transport through a metallic dot strongly coupled to a transmission line cavity
We investigate theoretically the properties of the photon state and the
electronic transport in a system consisting of a metallic quantum dot strongly
coupled to a superconducting microwave transmission line cavity. Within the
framework of circuit quantum electrodynamics we derive a Hamiltonian for
arbitrary strong capacitive coupling between the dot and the cavity. The
dynamics of the system is described by a quantum master equation, accounting
for the electronic transport as well as the coherent, non-equilibrium
properties of the photon state. The photon state is investigated, focusing on,
for a single active mode, signatures of microwave polaron formation and the
effects of a non-equilibrium photon distribution. For two active photon modes,
intra mode conversion and polaron coherences are investigated. For the
electronic transport, electrical current and noise through the dot and the
influence of the photon state on the transport properties are at the focus. We
identify clear transport signatures due to the non-equilibrium photon
population, in particular the emergence of superpoissonian shot-noise at
ultrastrong dot-cavity couplings.Comment: 19 pages, 10 figure
A Holographic Model of Strange Metals
We give a review on our recent work arXiv:1006.0779 [hep-th] and
arXiv:1006.1719 [hep-th], in which properties of holographic strange metals
were investigated. The background is chosen to be anisotropic scaling solution
in Einstein-Maxwell-Dilaton theory with a Liouville potential. The effects of
bulk Maxwell field, an extra U(1) gauge field and probe D-branes on the DC
conductivity, the DC Hall conductivity and the AC conductivity are extensively
analyzed. We classify behaviors of the conductivities according to the
parameter ranges in the bulk theory and characterize conditions when the
holographic results can reproduce experimental data.Comment: 34 pages, 15 figures, minor correction
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