295 research outputs found
Exploring gravitational theories beyond Horndeski
We have recently proposed a new class of gravitational scalar-tensor theories
free from Ostrogradski instabilities, in arXiv:1404.6495. As they generalize
Horndeski theories, or "generalized" galileons, we call them G. These
theories possess a simple formulation when the time hypersurfaces are chosen to
coincide with the uniform scalar field hypersurfaces. We confirm that they
contain only three propagating degrees of freedom by presenting the details of
the Hamiltonian formulation. We examine the coupling between these theories and
matter. Moreover, we investigate how they transform under a disformal
redefinition of the metric. Remarkably, these theories are preserved by
disformal transformations that depend on the scalar field gradient, which also
allow to map subfamilies of G into Horndeski theories.Comment: 33 pages, added comments and corrected typos as in JCAP versio
Process tomography of field damping and measurement of Fock state lifetimes by quantum non-demolition photon counting in a cavity
The relaxation of a quantum field stored in a high- superconducting cavity
is monitored by non-resonant Rydberg atoms. The field, subjected to repetitive
quantum non-demolition (QND) photon counting, undergoes jumps between photon
number states. We select ensembles of field realizations evolving from a given
Fock state and reconstruct the subsequent evolution of their photon number
distributions. We realize in this way a tomography of the photon number
relaxation process yielding all the jump rates between Fock states. The damping
rates of the photon states () are found to increase
linearly with . The results are in excellent agreement with theory including
a small thermal contribution
Entanglement of a Mesoscopic Field with an Atom induced by Photon Graininess in a Cavity
We observe that a mesoscopic field made of several tens of microwave photons
exhibits quantum features when interacting with a single Rydberg atom in a
high-Q cavity. The field is split into two components whose phases differ by an
angle inversely proportional to the square root of the average photon number.
The field and the atomic dipole are phase-entangled. These manifestations of
photon graininess vanish at the classical limit. This experiment opens the way
to studies of large Schrodinger cat states at the quantum-classical boundary
Phase space tweezers for tailoring cavity fields by quantum Zeno dynamics
We discuss an implementation of Quantum Zeno Dynamics in a Cavity Quantum
Electrodynamics experiment. By performing repeated unitary operations on atoms
coupled to the field, we restrict the field evolution in chosen subspaces of
the total Hilbert space. This procedure leads to promising methods for
tailoring non-classical states. We propose to realize `tweezers' picking a
coherent field at a point in phase space and moving it towards an arbitrary
final position without affecting other non-overlapping coherent components.
These effects could be observed with a state-of-the-art apparatus
Prewetting transition on a weakly disordered substrate : evidence for a creeping film dynamics
We present the first microscopic images of the prewetting transition of a
liquid film on a solid surface. Pictures of the local coverage map of a helium
film on a cesium metal surface are taken while the temperature is raised
through the transition. The film edge is found to advance at constant
temperature by successive avalanches in a creep motion with a macroscopic
correlation length. The creep velocity varies strongly in a narrow temperature
range. The retreat motion is obtained only at much lower temperature,
conforming to the strong hysteresis observed for prewetting transition on a
disordered surface. Prewetting transition on such disordered surfaces appears
to give rise to dynamical phenomena similar to what is observed for domain wall
motions in 2D magnets.Comment: 7 pages, 3 figures, to be published in Euro.Phys.Let
Implementation of stability-based transition model by means of transport equations
A natural laminar-turbulent transition model compatible with Computation Fluid Dynamics is presented. This model accounts for longitudinal transition mechanisms (i.e. Tollmien-Schlichting induced transition) thanks to systematic stability computation on similar boundary profiles from Mach zero to four both on adiabatic and isothermal wall. The model embeds as well the so-called “C1-criterion” for transverse transition mechanisms (i.e. cross-flow waves induced transition). The transition model is written under transport equations formalism and has been implemented in the solver elsA (ONERA-Airbus-Safran property). Validations are performed on three dimensional configurations and comparisons are shown against a database method for natural transition modeling and experiments
Nonprobabilistic teleportation of field state via cavity QED
In this article we discuss a teleportation scheme of coherent states of
cavity field. The experimental realization proposed makes use of cavity quatum
electrodynamics involving the interaction of Rydberg atoms with micromaser and
Ramsey cavities. In our scheme the Ramsey cavities and the atoms play the role
of auxiliary systems used to teleport the state from a micromaser cavity to
another. We show that, even if the correct atomic detection fails in the first
trials, one can succeed in teleportating the cavity field state if the proper
measurement occurs in a later atom
Degenerate higher order scalar-tensor theories beyond Horndeski up to cubic order
We present all scalar-tensor Lagrangians that are cubic in second derivatives of a scalar field, and that are degenerate, hence avoiding Ostrogradsky instabilities. Thanks to the existence of constraints, they propagate no more than three degrees of freedom, despite having higher order equations of motion. We also determine the viable combinations of previously identified quadratic degenerate Lagrangians and the newly established cubic ones. Finally, we study whether the new theories are connected to known scalar-tensor theories such as Horndeski and beyond Horndeski, through conformal or disformal transformations
Preparation of Long-Lived, Non-Autoionizing Circular Rydberg States of Strontium
Alkaline earth Rydberg atoms are very promising tools for quantum
technologies. Their highly excited outer electron provides them with the
remarkable properties of Rydberg atoms and, notably, with a huge coupling to
external fields or to other Rydberg atoms while the ionic core retains an
optically active electron. However, low angular-momentum Rydberg states suffer
almost immediate autoionization when the core is excited. Here, we demonstrate
that strontium circular Rydberg atoms with a core excited in a metastable
level are impervious to autoionization over more than a few millisecond time
scale. This makes it possible to trap and laser-cool Rydberg atoms. Moreover,
we observe singlet to triplet transitions due to the core optical
manipulations, opening the way to a quantum microwave to optical interface
Quantum Zeno dynamics of a field in a cavity
We analyze the quantum Zeno dynamics that takes place when a field stored in
a cavity undergoes frequent interactions with atoms. We show that repeated
measurements or unitary operations performed on the atoms probing the field
state confine the evolution to tailored subspaces of the total Hilbert space.
This confinement leads to non-trivial field evolutions and to the generation of
interesting non-classical states, including mesoscopic field state
superpositions. We elucidate the main features of the quantum Zeno mechanism in
the context of a state-of-the-art cavity quantum electrodynamics experiment. A
plethora of effects is investigated, from state manipulations by phase space
tweezers to nearly arbitrary state synthesis. We analyze in details the
practical implementation of this dynamics and assess its robustness by
numerical simulations including realistic experimental imperfections. We
comment on the various perspectives opened by this proposal
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