404,516 research outputs found
Moving system with speeded-up evolution
In the classical (non-quantum) relativity theory the course of the moving
clock is dilated as compared to the course of the clock at rest (the Einstein
dilation). Any unstable system may be regarded as a clock. The time evolution
(e.g., the decay) of a uniformly moving physical system is considered using the
relativistic quantum theory. The example of a moving system is given whose
evolution turns out to be speeded-up instead of being dilated. A discussion of
this paradoxical result is presented.Comment: 10 pages, LaTe
Collisionally Induced Atomic Clock Shifts and Correlations
We develop a formalism to incorporate exchange symmetry considerations into
the calculation of collisional frequency shifts and blackbody radiation effects
for atomic clock transitions using a density matrix formalism. The formalism is
developed for both fermionic and bosonic atomic clocks. Results for a finite
temperature Sr () atomic clock in a magic
wavelength optical lattice are presented.Comment: 11 pages, 9 figures. Physical Review A (in press
Conformal proper times according to the Woodhouse causal axiomatics of relativistic spacetimes
On the basis of the Woodhouse causal axiomatics, we show that conformal
proper times and an extra variable in addition to those of space and time,
precisely and physically identified from experimental examples, together give a
physical justification for the `chronometric hypothesis' of general relativity.
Indeed, we show that, with a lack of these latter two ingredients, no clock
paradox solution exists in which the clock and message functions are solely at
the origin of the asymmetry. These proper times originate from a given
conformal structure of the spacetime when ascribing different compatible
projective structures to each Woodhouse particle, and then, each defines a
specific Weylian sheaf structure. In addition, the proper time
parameterizations, as two point functions, cannot be defined irrespective of
the processes in the relative changes of physical characteristics. These
processes are included via path-dependent conformal scale factors, which act
like sockets for any kind of physical interaction and also represent the values
of the variable associated with the extra dimension. As such, the differential
aging differs far beyond the first and second clock effects in Weyl geometries,
with the latter finally appearing to not be suitable.Comment: 25 pages, 2 figure
Teleportation transfers only speakable quantum information
We show that a quantum clock cannot be teleported without prior
synchronization between sender and receiver: every protocol using a finite
amount of entanglement and an arbitrary number of rounds of classical
communication will necessarily introduce an error in the teleported state of
the clock. Nevertheless, we show that entanglement can be used to achieve
synchronization with precision higher than any classical correlation allows,
and we give the optimized strategy for this task. The same results hold also
for arbitrary continuous quantum reference frames, which encode general
unspeakable information,-information that cannot be encoded into a number, but
instead requires a specific physical support, like a clock or a gyroscope, to
be conveyed.Comment: 5 pages, no figures, published versio
Frequency ratios of Sr, Yb and Hg based optical lattice clocks and their applications
This article describes the recent progress of optical lattice clocks with
neutral strontium (Sr), ytterbium (Yb) and mercury (Hg)
atoms. In particular, we present frequency comparison between the clocks
locally via an optical frequency comb and between two Sr clocks at remote sites
using a phase-stabilized fibre link. We first review cryogenic Sr optical
lattice clocks that reduce the room-temperature blackbody radiation shift by
two orders of magnitude and serve as a reference in the following clock
comparisons. Similar physical properties of Sr and Yb atoms, such as transition
wavelengths and vapour pressure, have allowed our development of a compatible
clock for both species. A cryogenic Yb clock is evaluated by referencing a Sr
clock. We also report on a Hg clock, which shows one order of magnitude less
sensitivity to blackbody radiation, while its large nuclear charge makes the
clock sensitive to the variation of fine-structure constant. Connecting all
three types of clocks by an optical frequency comb, the ratios of the clock
frequencies are determined with uncertainties smaller than possible through
absolute frequency measurements. Finally, we describe a synchronous frequency
comparison between two Sr-based remote clocks over a distance of 15 km between
RIKEN and the University of Tokyo, as a step towards relativistic geodesy.Comment: 11 pages, 5 figures, invited review article in Comptes Rendus de
Physique 201
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