18,555 research outputs found
Quantum clocks observe classical and quantum time dilation
At the intersection of quantum theory and relativity lies the possibility of
a clock experiencing a superposition of proper times. We consider quantum
clocks constructed from the internal degrees of relativistic particles that
move through curved spacetime. The probability that one clock reads a given
proper time conditioned on another clock reading a different proper time is
derived. From this conditional probability distribution, it is shown that when
the center-of-mass of these clocks move in localized momentum wave packets they
observe classical time dilation. We then illustrate a quantum correction to the
time dilation observed by a clock moving in a superposition of localized
momentum wave packets that has the potential to be observed in experiment. The
Helstrom-Holevo lower bound is used to derive a proper time-energy/mass
uncertainty relation.Comment: Updated to match published versio
Communication between inertial observers with partially correlated reference frames
In quantum communication protocols the existence of a shared reference frame
between two spatially separated parties is normally presumed. However, in many
practical situations we are faced with the problem of misaligned reference
frames. In this paper, we study communication between two inertial observers
who have partial knowledge about the Lorentz transformation that relates their
frames of reference. Since every Lorentz transformation can be decomposed into
a pure boost followed by a rotation, we begin by analysing the effects on
communication when the parties have partial knowledge about the transformation
relating their frames, when the transformation is either a rotation or pure
boost. This then enables us to investigate how the efficiency of communication
is affected due to partially correlated inertial reference frames related by an
arbitrary Lorentz transformation. Furthermore, we show how the results of
previous studies where reference frames are completely uncorrelated are
recovered from our results in appropriate limits.Comment: 9 pages, 3 figures, typos corrected, figures update
Spacetime structure and vacuum entanglement
We study the role that both vacuum fluctuations and vacuum entanglement of a
scalar field play in identifying the spacetime topology, which is not
prescribed from first principles---neither in general relativity or quantum
gravity. We analyze how the entanglement and observable correlations acquired
between two particle detectors are sensitive to the spatial topology of
spacetime. We examine the detector's time evolution to all orders in
perturbation theory and then study the phenomenon of vacuum entanglement
harvesting in Minkowski spacetime and two flat topologically distinct
spacetimes constructed from identifications of the Minkowski space. We show
that, for instance, if the spatial topology induces a preferred direction, this
direction may be inferred from the dependence of correlations between the two
detectors on their orientation. We therefore show that vacuum fluctuations and
vacuum entanglement harvesting makes it, in principle, possible to distinguish
spacetimes with identical local geometry that differ only in their topology
Investigation of mixed element hybrid grid-based CFD methods for rotorcraft flow analysis
Accurate first-principles flow prediction is essential to the design and development of rotorcraft, and while current numerical analysis tools can, in theory, model the complete flow field, in practice the accuracy of these tools is limited by various inherent numerical deficiencies. An approach that combines the first-principles physical modeling capability of CFD schemes with the vortex preservation capabilities of Lagrangian vortex methods has been developed recently that controls the numerical diffusion of the rotor wake in a grid-based solver by employing a vorticity-velocity, rather than primitive variable, formulation. Coupling strategies, including variable exchange protocols are evaluated using several unstructured, structured, and Cartesian-grid Reynolds Averaged Navier-Stokes (RANS)/Euler CFD solvers. Results obtained with the hybrid grid-based solvers illustrate the capability of this hybrid method to resolve vortex-dominated flow fields with lower cell counts than pure RANS/Euler methods
Proposal for an Optical Test of the Einstein Equivalence Principle
The Einstein Equivalence Principle (EEP) underpins all metric theories of
gravity. Its key element is the local position invariance of non-gravitational
experiments, which entails the gravitational red-shift. Precision measurements
of the gravitational red-shift tightly bound violations of the EEP only in the
fermionic sector of the Standard Model, however recent developments of
satellite optical technologies allow for its investigation in the
electromagnetic sector. Proposals exploiting light interferometry traditionally
suffer from the first-order Doppler effect, which dominates the weak
gravitational signal necessary to test the EEP, making them unfeasible. Here,
we propose a novel scheme to test the EEP, which is based on a double
large-distance optical interferometric measurement. By manipulating the
phase-shifts detected at two locations at different gravitational potentials it
is possible to cancel-out the first-order Doppler effect and observe the
gravitational red-shift implied by the EEP. We present the detailed analysis of
the proposal within the post-Newtonian framework and the simulations of the
expected signals obtained by using two realistic satellite orbits. Our proposal
to overcome the first-order Doppler effect in optical EEP tests is feasible
with current technology.Comment: manuscript improve
Effect of relativistic acceleration on localized two-mode Gaussian quantum states
We study how an arbitrary Gaussian state of two localized wave packets,
prepared in an inertial frame of reference, is described by a pair of uniformly
accelerated observers. We explicitly compute the resulting state for
arbitrarily chosen proper accelerations of the observers and independently
tuned distance between them. To do so, we introduce a generalized Rindler frame
of reference and analytically derive the corresponding state transformation as
a Gaussian channel. Our approach provides several new insights into the
phenomenon of vacuum entanglement such as the highly non-trivial effect of
spatial separation between the observers including sudden death of
entanglement. We also calculate the fidelity of the two-mode channel for
non-vacuum Gaussian states and obtain bounds on classical and quantum
capacities of a single-mode channel. Our framework can be directly applied to
any continuous variable quantum information protocol in which the effects of
acceleration or gravity cannot be neglected.Comment: 21 pages, 13 figures. A few typos correcte
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