160 research outputs found
Progress on testing Lorentz symmetry with MICROSCOPE
The Weak Equivalence Principle (WEP) and the local Lorentz invariance (LLI)
are two major assumptions of General Relativity (GR). The MICROSCOPE mission,
currently operating, will perform a test of the WEP with a precision of
. The data will also be analysed at SYRTE for the purposes of a LLI
test realised in collaboration with J. Tasson (Carleton College, Minnesota) and
Q. Bailey (Embry-Riddle Aeronautical University, Arizona). This study will be
performed in a general framework, called the Standard Model Extension (SME),
describing Lorentz violations that could appear at Planck scale (
GeV). The SME allows us to derive a Lorentz violating observable designed for
the MICROSCOPE experiment and to search for possible deviations from LLI in the
differential acceleration of the test masses
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
Dynamical coupling between a Bose-Einstein condensate andacavity optical lattice
A Bose-Einstein condensate is dispersively coupled to a single mode of an ultra-high finesse optical cavity. The system is governed by strong interactions between the atomic motion and the light field even at the level of single quanta. While coherently pumping the cavity mode the condensate is subject to the cavity optical lattice potential whose depth depends nonlinearly on the atomic density distribution. We observe optical bistability already below the single photon level and strong back-action dynamics which tunes the coupled system periodically out of resonanc
Extension of Information Geometry to Non-statistical Systems: Some Examples
Our goal is to extend information geometry to situations where statistical
modeling is not obvious. The setting is that of modeling experimental data.
Quite often the data are not of a statistical nature. Sometimes also the model
is not a statistical manifold. An example of the former is the description of
the Bose gas in the grand canonical ensemble. An example of the latter is the
modeling of quantum systems with density matrices. Conditional expectations in
the quantum context are reviewed. The border problem is discussed: through
conditioning the model point shifts to the border of the differentiable
manifold.Comment: 8 pages, to be published in the proceedings of GSI2015, Lecture Notes
in Computer Science, Springe
Manipulating a qubit through the backaction of sequential partial measurements and real-time feedback
Quantum measurements not only extract information from a system but also
alter its state. Although the outcome of the measurement is probabilistic, the
backaction imparted on the measured system is accurately described by quantum
theory. Therefore, quantum measurements can be exploited for manipulating
quantum systems without the need for control fields. We demonstrate
measurement-only state manipulation on a nuclear spin qubit in diamond by
adaptive partial measurements. We implement the partial measurement via tunable
correlation with an electron ancilla qubit and subsequent ancilla readout. We
vary the measurement strength to observe controlled wavefunction collapse and
find post-selected quantum weak values. By combining a novel quantum
non-demolition readout on the ancilla with real-time adaption of the
measurement strength we realize steering of the nuclear spin to a target state
by measurements alone. Besides being of fundamental interest, adaptive
measurements can improve metrology applications and are key to
measurement-based quantum computing.Comment: 6 pages, 4 figure
Mapping the optimal route between two quantum states
A central feature of quantum mechanics is that a measurement is intrinsically
probabilistic. As a result, continuously monitoring a quantum system will
randomly perturb its natural unitary evolution. The ability to control a
quantum system in the presence of these fluctuations is of increasing
importance in quantum information processing and finds application in fields
ranging from nuclear magnetic resonance to chemical synthesis. A detailed
understanding of this stochastic evolution is essential for the development of
optimized control methods. Here we reconstruct the individual quantum
trajectories of a superconducting circuit that evolves in competition between
continuous weak measurement and driven unitary evolution. By tracking
individual trajectories that evolve between an arbitrary choice of initial and
final states we can deduce the most probable path through quantum state space.
These pre- and post-selected quantum trajectories also reveal the optimal
detector signal in the form of a smooth time-continuous function that connects
the desired boundary conditions. Our investigation reveals the rich interplay
between measurement dynamics, typically associated with wave function collapse,
and unitary evolution of the quantum state as described by the Schrodinger
equation. These results and the underlying theory, based on a principle of
least action, reveal the optimal route from initial to final states, and may
enable new quantum control methods for state steering and information
processing.Comment: 12 pages, 9 figure
Dynamical Coupling between a Bose-Einstein Condensate and a Cavity Optical Lattice
A Bose-Einstein condensate is dispersively coupled to a single mode of an
ultra-high finesse optical cavity. The system is governed by strong
interactions between the atomic motion and the light field even at the level of
single quanta. While coherently pumping the cavity mode the condensate is
subject to the cavity optical lattice potential whose depth depends nonlinearly
on the atomic density distribution. We observe bistability already below the
single photon level and strong back-action dynamics which tunes the system
periodically out of resonance.Comment: 5 pages, 4 figure
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