Features of Rashba-coupled Fermi gases, master equations and memory effects

The first part of this thesis studies interactions in Rashba-coupled Fermi gases. The main objective of this part of the thesis consists of proposing a model to describe dilute Fermi gases. Recent theoretical works propose to use Rashba spin-orbit-coupled systems by means to enhance superconductivity, topologically protected insulators, or quantum computing. The richness and potential of Rashba-coupled Fermi systems has been proved with currently ongoing experiments with cold atoms and synthetic gauge fields, which allow to simulate neutral particles using laser fields. In this part of the thesis, we conclude that it is possible to describe dilute Rashba-coupled Fermi gases with a model that has meaningful predictive power. In the second part of the thesis we analyse the validity of the master equation approach to describe open quantum systems. Using a Jaynes-Cummings Hamiltonian we show that under certain circumstances, the master equation approach does not fully describe the effect of the environment onto the system, hence additional tools are needed

Investigating the generality of time-local master equations

Time-local master equations are more generally applicable than is often recognised, but at first sight it would seem that they can only safely be used in time intervals where the time evolution is invertible. Using the Jaynes-Cummings model, we here construct an explicit example where two different Hamiltonians, corresponding to two different non-invertible and non-Markovian time evolutions, will lead to arbitrarily similar time-local master equations. This illustrates how the time-local master equation on its own in this case does not uniquely determine the time evolution. The example is nevertheless artificial in the sense that a rapid change in (at least) one of the Hamiltonians is needed. The change must also occur at a very specific instance in time. If a Hamiltonian is known not to have such very specific behaviour, but is "physically well-behaved", then one may conjecture that a time-local master equation also determines the time evolution when it is not invertible.Comment: 7 pages, 6 figure

Non-Galilean response of Rashba coupled Fermi gases

We consider the effect of a momentum kick on the ground state of a non-interacting two-dimensional Fermi gas subject to Rashba spin-orbit coupling. Although the total momentum is a constant of motion, the gas does not obey the rules of Galilean relativity. Upon imprinting a small overall velocity to the non-interacting gas, we find that the Fermi sea is deformed in a non-trivial way. We also consider a weakly repulsive Fermi gas, and find, from its Hartree shift, that the total ground state of the system may change into a deformed, finite momentum ground state as the repulsion is increased beyond a critical value, without the need of any external Zeeman fields. We also discuss possible experimental signatures of these effects.Comment: 6 pages, 1 figure. Published versio

Signal detection without finite-energy limits to quantum resolution

We show that there are extremely simple signal detection schemes where the finiteness of energy resources places no limit to the resolution. On the contrary, larger resolution can be obtained with lower energy. To this end the generator of the signal-dependent transformation encoding the signal information on the probe state must be different from the energy. We show that the larger the deviation of the probe state from being minimum-uncertainty state, the better the resolution.Comment: 5 pages, 3 figure

Condiciones de protección radiológica en el departamento de radiología e imágenes del Hospital de Neumología y Medicina Familiar “Dr. José Antonio Saldaña” en el periodo comprendido de enero a julio de 2018

La presente investigación denominada condiciones de protección radiológica en el Departamento de Radiología e Imágenes del Hospital de Neumología y Medicina Familiar Dr. José Antonio Saldaña busca recopilar la información del área de dicho departamento ya que es una investigación de tipo descriptiva detallando cada una de las condiciones de protección con las que cuenta el departamento lo que hace más conveniente y beneficioso en pacientes y personal ocupacionalmente expuesto

Advances in quantum metrology

The statistical error in any estimation can be reduced by repeating the measurement and averaging the results. The central limit theorem implies that the reduction is proportional to the square root of the number of repetitions. Quantum metrology is the use of quantum techniques such as entanglement to yield higher statistical precision than purely classical approaches. In this Review, we analyse some of the most promising recent developments of this research field and point out some of the new experiments. We then look at one of the major new trends of the field: analyses of the effects of noise and experimental imperfections

Investigating the generality of time-local master equations

We acknowledge helpful discussions with J. Cresser. D.M.-M. acknowledges support from the EPSRC CMDTC,P.O. acknowledges support from EPSRC Grant No. EP/J001392/1, B.W.L. thanks the Royal Society for a University Research Fellowship, and E.A. acknowledges partial support from EPSRC Grant No. EP/G009821/1.Time-local master equations are more generally applicable than is often recognized, but at first sight, it would seem that they can only safely be used in time intervals where the time evolution is invertible. Using the Jaynes-Cummings model, we here construct an explicit example where two different Hamiltonians, corresponding to two different noninvertible and non-Markovian time evolutions, lead to arbitrarily similar time-local master equations. This illustrates how the time-local master equation, on its own in this case, does not uniquely determine the time evolution. The example is, nevertheless, artificial in the sense that a rapid change in (at least) one of the Hamiltonians is needed. The change must also occur at a very specific instance in time. If a Hamiltonian is known not to have such very specific behavior but is "physically well behaved," then one may conjecture that a time-local master equation also determines the time evolution when it is not invertible.Publisher PDFPeer reviewe

Metrological resolution and minimum uncertainty states in linear and nonlinear signal detection schemes

We study the performance of linear and nonlinear optical schemes for the detection of weak signals for two classes of probe states. These are quadrature coherent squeezed states and the minimum uncertainty states of the generator of the transformation and the measured observable. Both for linear and nonlinear schemes we show that the generator-measurement minimum uncertainty states are far from being optimum, while the quadrature coherent squeezed states can reach maximum accuracy almost for the same amount of squeezing in both cases. The analysis is largely based on a suitable approximation treating the photon number as a continuous variable