107 research outputs found

### On the consequences of the fact that atomic levels have a certain width

This note presents two ideas. The first one is that quantum theory has a
fundamentally perturbative basis but leads to nonperturbative states which it
would seem natural to take into account in the foundation of a theory of
quantum phenomena. The second one consists in questioning the validity of the
present notion of time. Both matters are related to the fact that atomic levels
have a certain width. This note is presented qualitatively so as to evidence
its main points, independently of the models on which these have been tested.Comment: 8 page

### Physique atomique et moléculaire, 1973-2004

Publications Wolf P., Blanchet L., Bordé C.J., Reynaud S., Salomon C. et Cohen-Tannoudji C., « Reply to the comment on ‘Does an atom interferometer test the gravitational redshift at the Compton frequency?’« , Class. Quantum Grav., 29, 2012, 048002. Wassen W., Cohen-Tannoudji C., Leduc M., Boiron D., Westbrook C.I., Truscott A., Baldwin K., Birkl G., Cancio P., Trippenbach M., « Cold and trapped metastable noble gases », Rev. Mod. Phys., 84, 2012, 175. Ouvrages Cohen-Tannoudji C. et Guéry-Ode..

### The evolution of free wave packets

We discuss four general features of force-free evolution: (1) The spatial
spread of any packet changes with time in a very simple way. (2) Over
sufficiently short periods of time (whose duration is related to the spread in
momentum of the packet) the probability distribution moves but there is little
change in shape. (3) After a sufficiently long period (related to the initial
spatial spread) the packet settles into a simple form simply related to the
momentum distribution in the packet. In this asymptotic regime, the shape of
the probability distribution no longer changes except for its scale, which
increases linearly with the time. (4) There is an infinite denumerable set of
simple wave packets (the Hermite-Gauss packets) that do not change shape as
they evolve.Comment: 6 pages, 4 figures, didactic pape

### Does an atom interferometer test the gravitational redshift at the Compton frequency ?

Atom interferometers allow the measurement of the acceleration of freely
falling atoms with respect to an experimental platform at rest on Earth's
surface. Such experiments have been used to test the universality of free fall
by comparing the acceleration of the atoms to that of a classical freely
falling object. In a recent paper, M\"uller, Peters and Chu [Nature {\bf 463},
926-929 (2010)] argued that atom interferometers also provide a very accurate
test of the gravitational redshift when considering the atom as a clock
operating at the Compton frequency associated with the rest mass. We analyze
this claim in the frame of general relativity and of different alternative
theories. We show that the difference of "Compton phases" between the two paths
of the interferometer is actually zero in a large class of theories, including
general relativity, all metric theories of gravity, most non-metric theories
and most theoretical frameworks used to interpret the violations of the
equivalence principle. Therefore, in most plausible theoretical frameworks,
there is no redshift effect and atom interferometers only test the universality
of free fall. We also show that frameworks in which atom interferometers would
test the redshift pose serious problems, such as (i) violation of the Schiff
conjecture, (ii) violation of the Feynman path integral formulation of quantum
mechanics and of the principle of least action for matter waves, (iii)
violation of energy conservation, and more generally (iv) violation of the
particle-wave duality in quantum mechanics. Standard quantum mechanics is no
longer valid in such frameworks, so that a consistent interpretation of the
experiment would require an alternative formulation of quantum mechanics. As
such an alternative has not been proposed to date, we conclude that the
interpretation of atom interferometers as testing the gravitational redshift is
unsound.Comment: 26 pages. Modified version to appear in Classical and Quantum Gravit

### Donor-donor interaction mediated by cavity-photons and its relation to interactions mediated by excitons and polaritons

I report theoretical predictions of two models of donor-donor indirect
interaction mediated by photons in zero- and two-dimensional cavities. These
results are compared to previously studied cases of indirect interactions
mediated by excitons and/or polaritons in bulk semiconductor and
two-dimensional cavities. I find that photons mediate an Ising-like interaction
between donors in the same manner polaritons do, in contrast to the
Heisenberg-like interaction mediated by exciton. For the particular case of a
two-dimensional cavity, the model shows that the dependence on distance of the
donor-donor coupling constant is the same for photons and polaritons when the
donor-donor distance is large. Then, it becomes clear that photons are
responsible for the long range behavior of the polariton indirect interaction

### General limit to non-destructive optical detection of atoms

We demonstrate that there is a fundamental limit to the sensitivity of
phase-based detection of atoms with light for a given maximum level of
allowable spontaneous emission. This is a generalisation of previous results
for two-level and three-level atoms. The limit is due to an upper bound on the
phase shift that can be imparted on a laser beam for a given excited state
population. Specifially, we show that no single-pass optical technique using
classical light, based on any number of lasers or coherences between any number
of levels, can exceed the limit imposed by the two-level atom. This puts
significant restrictions on potential non-destructive optical measurement
schemes.Comment: 7 pages, 1 figur

### Twisted-light-induced optical transitions in semiconductors: Free-carrier quantum kinetics

We theoretically investigate the interband transitions and quantum kinetics
induced by light carrying orbital angular momentum, or twisted light, in bulk
semiconductors. We pose the problem in terms of the Heisenberg equations of
motion of the electron populations, and inter- and intra-band coherences. Our
theory extends the free-carrier Semiconductor Bloch Equations to the case of
photo-excitation by twisted light. The theory is formulated using cylindrical
coordinates, which are better suited to describe the interaction with twisted
light than the usual cartesian coordinates used to study regular optical
excitation. We solve the equations of motion in the low excitation regime, and
obtain analytical expressions for the coherences and populations; with these,
we calculate the orbital angular momentum transferred from the light to the
electrons and the paramagnetic and diamagnetic electric current densities.Comment: 11 pages, 3 figure

### Analytical solutions for a two-level system driven by a class of chirped pulses

We present analytical solutions for the problem of a two-level atom driven by
a class of chirped pulses. The solutions are given in terms of Heun functions.
Using appropriate chirping parameters an enhancement of four-orders of
magnitudes in the population transfer is obtained.Comment: 5 pages, 5 figure

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