105 research outputs found
Experimental method for measuring classical concurrence of generic beam shapes
Classical entanglement is a powerful tool which provides a neat numerical
estimate for the study of classical correlations. Its experimental
investigation, however, has been limited to special cases. Here, we demonstrate
that the experimental quantification of the level of classical entanglement can
be carried out in more general instances. Our approach enables the extension to
arbitrarily shaped transverse modes and hence delivering a suitable
quantification tool to describe concisely the modal structure
Electric dipole moment searches: reexamination of frequency shifts for particles in traps
In experiments searching for a nonzero electric dipole moment of trapped
particles, frequency shifts correlated with an applied electric field can be
interpreted as a false signal. One such effect, referred to as the geometric
phase effect, is known to occur in a magnetic field that is nonperfectly
homogeneous. The increase in sensitivity of experiments demands improved
theoretical description of this effect. In the case of fast particles, like
atoms at room temperature and low pressure, the validity of established
theories was limited to a cylindrical confinement cell in a uniform gradient
with cylindrical symmetry. We develop a more general theory valid for an
arbitrary shape of the magnetic field as well as for arbitrary geometry of the
confinement cell. Our improved theory is especially relevant for experiments
measuring the neutron electric dipole moment with an atomic comagnetometer. In
this context, we have reproduced and extended earlier numerical studies of the
geometric phase effect induced by localized magnetic impurities
Geometrical bounds on irreversibility in open quantum systems
Clausius inequality has deep implications for reversibility and the arrow of
time. Quantum theory is able to extend this result for closed systems by
inspecting the trajectory of the density matrix on its manifold. Here we show
that this approach can provide an upper and lower bound to the irreversible
entropy production for open quantum systems as well. These provide insights on
the thermodynamics of the information erasure. Limits of the applicability of
our bounds are discussed, and demonstrated in a quantum photonic simulator
Bridging thermodynamics and metrology in non-equilibrium Quantum Thermometry
Single-qubit thermometry presents the simplest tool to measure the
temperature of thermal baths with reduced invasivity. At thermal equilibrium,
the temperature uncertainty is linked to the heat capacity of the qubit,
however the best precision is achieved outside equilibrium condition. Here, we
discuss a way to generalize this relation in a non-equilibrium regime, taking
into account purely quantum effects such as coherence. We support our findings
with an experimental photonic simulation.Comment: 7 pages, 4 figure
Information-reality complementarity in photonic weak measurements
The emergence of realistic properties is a key problem in understanding the quantum-to-classical transition. In this respect, measurements represent a way to interface quantum systems with the macroscopic world: these can be driven in the weak regime, where a reduced back-action can be imparted by choosing meter states able to extract different amounts of information. Here we explore the implications of such weak measurement for the variation of realistic properties of two-level quantum systems pre- and postmeasurement, and extend our investigations to the case of open systems implementing the measurements
The half-life of Fr in Si and Au at 4K and at mK temperatures
The half-life of the decaying nucleus Fr was determined in
different environments, i.e. embedded in Si at 4 K, and embedded in Au at 4 K
and about 20 mK. No differences in half-life for these different conditions
were observed within 0.1%. Furthermore, we quote a new value for the absolute
half-life of Fr of t = 286.1(10) s, which is of comparable
precision to the most precise value available in literature
Precision measurements of the Co -asymmetry parameter in search for tensor currents in weak interactions
The -asymmetry parameter for the Gamow-Teller decay of
Co was measured by polarizing the radioactive nuclei with the brute
force low-temperature nuclear-orientation method. The Co activity was
cooled down to milliKelvin temperatures in a He-He dilution
refrigerator in an external 13 T magnetic field. The particles were
observed by a 500 thick Si PIN diode operating at a temperature of
about 10 K in a magnetic field of 0.6 T. Extensive GEANT4 Monte-Carlo
simulations were performed to gain control over the systematic effects. Our
result, , is in agreement with
the Standard-Model value of , which includes recoil-order
corrections that were addressed for the first time for this isotope. Further,
it enables limits to be placed on possible tensor-type charged weak currents as
well as other physics beyond the Standard Model
The entropic cost of quantum generalized measurements
Landauer’s principle introduces a symmetry between computational and physical processes: erasure of information, a logically irreversible operation, must be underlain by an irreversible transformation dissipating energy. Monitoring micro- and nano-systems needs to enter into the energetic balance of their control; hence, finding the ultimate limits is instrumental to the development of future thermal machines operating at the quantum level. We report on the experimental investigation of a lower bound to the irreversible entropy associated to generalized quantum measurements on a quantum bit. We adopted a quantum photonics gate to implement a device interpolating from the weakly disturbing to the fully invasive and maximally informative regime. Our experiment prompted us to introduce a bound taking into account both the classical result of the measurement and the outcoming quantum state; unlike previous investigation, our entropic bound is based uniquely on measurable quantities. Our results highlight what insights the information-theoretic approach provides on building blocks of quantum information processors
Average ground-state energy of finite Fermi systems
Semiclassical theories like the Thomas-Fermi and Wigner-Kirkwood methods give
a good description of the smooth average part of the total energy of a Fermi
gas in some external potential when the chemical potential is varied. However,
in systems with a fixed number of particles N, these methods overbind the
actual average of the quantum energy as N is varied. We describe a theory that
accounts for this effect. Numerical illustrations are discussed for fermions
trapped in a harmonic oscillator potential and in a hard wall cavity, and for
self-consistent calculations of atomic nuclei. In the latter case, the
influence of deformations on the average behavior of the energy is also
considered.Comment: 10 pages, 8 figure
qBounce: Systematic shifts of transition frequencies of gravitational states of ultra-cold neutrons using Ramsey gravity resonance spectroscopy
qBounce is using quantum states of ultra-cold neutrons in the gravitational
field of the Earth to investigate gravitation in the micrometre range. We
present current measurements taken in 2021 at the Institut Laue-Langevin (ILL)
to determine energy differences of these states by mechanically induced
transitions. This allows a determination of the local acceleration using a
quantum measurement. The data presented here results in .
The classical local value at the experiment is . We present
an analysis of systematic effects that induces shifts of the transition
frequency of order 100 mHz. The inferred value for at the experiment shows
a systematic shift of
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