Influence of the detector's temperature on the quantum Zeno effect

In this paper we study the quantum Zeno effect using the irreversible model of the measurement. The detector is modeled as a harmonic oscillator interacting with the environment. The oscillator is subjected to the force, proportional to the energy of the measured system. We use the Lindblad-type master equation to model the interaction with the environment. The influence of the detector's temperature on the quantum Zeno effect is obtained. It is shown that the quantum Zeno effect becomes stronger (the jump probability decreases) when the detector's temperature increases

Precision spectroscopy with two correlated atoms

We discuss techniques that allow for long coherence times in laser spectroscopy experiments with two trapped ions. We show that for this purpose not only entangled ions prepared in decoherence-free subspaces can be used but also a pair of ions that are not entangled but subject to the same kind of phase noise. We apply this technique to a measurement of the electric quadrupole moment of the 3d D5/2 state of 40Ca+ and to a measurement of the linewidth of an ultrastable laser exciting a pair of 40Ca+ ions

Quantum Zeno effect in a probed downconversion process

The distorsion of a spontaneous downconvertion process caused by an auxiliary mode coupled to the idler wave is analyzed. In general, a strong coupling with the auxiliary mode tends to hinder the downconversion in the nonlinear medium. On the other hand, provided that the evolution is disturbed by the presence of a phase mismatch, the coupling may increase the speed of downconversion. These effects are interpreted as being manifestations of quantum Zeno or anti-Zeno effects, respectively, and they are understood by using the dressed modes picture of the device. The possibility of using the coupling as a nontrivial phase--matching technique is pointed out.Comment: 11 pages, 4 figure

Output spectrum of a detector measuring quantum oscillations

We consider a two-level quantum system (qubit) which is continuously measured by a detector and calculate the spectral density of the detector output. In the weakly coupled case the spectrum exhibits a moderate peak at the frequency of quantum oscillations and a Lorentzian-shape increase of the detector noise at low frequency. With increasing coupling the spectrum transforms into a single Lorentzian corresponding to random jumps between two states. We prove that the Bayesian formalism for the selective evolution of the density matrix gives the same spectrum as the conventional master equation approach, despite the significant difference in interpretation. The effects of the detector nonideality and the finite-temperature environment are also discussed.Comment: 8 pages, 6 figure

Spacetime Coarse Grainings in the Decoherent Histories Approach to Quantum Theory

We investigate the possibility of assigning consistent probabilities to sets of histories characterized by whether they enter a particular subspace of the Hilbert space of a closed system during a given time interval. In particular we investigate the case that this subspace is a region of the configuration space. This corresponds to a particular class of coarse grainings of spacetime regions. We consider the arrival time problem and the problem of time in reparametrization invariant theories as for example in canonical quantum gravity. Decoherence conditions and probabilities for those application are derived. The resulting decoherence condition does not depend on the explicit form of the restricted propagator that was problematic for generalizations such as application in quantum cosmology. Closely related is the problem of tunnelling time as well as the quantum Zeno effect. Some interpretational comments conclude, and we discuss the applicability of this formalism to deal with the arrival time problem.Comment: 23 pages, Few changes and added references in v

Optical-to-microwave frequency comparison with fractional uncertainty of 10(-15)

We report the technical aspects of the optical-to-microwave comparison for our recent measurements of the optical frequency of the mercury single-ion frequency standard in terms of the SI second as realized by the NIST-F1 cesium fountain clock. Over the course of six years, these measurements have resulted in a determination of the mercury single-ion frequency with a fractional uncertainty of less than 7x10(-16), making it the most accurately measured optical frequency to date. In this paper, we focus on the details of the comparison techniques used in the experiment and discuss the uncertainties associated with the optical-to-microwave synthesis based on a femtosecond laser frequency comb. We also present our most recent results in the context of the previous measurements of the mercury single-ion frequency and arrive at a final determination of the mercury single-ion optical frequency: f(Hg+)= 1064721 609 899 145.30(69) Hz

Lympho-geographical concepts in vaccine delivery

The key triggers and regulators of immune responses are antigens and their appearance in immune-privileged secondary lymphatic organs. Currently, the majority of vaccines are administered intramuscularly or subcutaneously, although neither the muscular tissue nor the subcutis is particularly rich in immuno-competent cells. Thus, introducing antigens at sites with a higher density of immune-competent cells, such as the dermis, lymph nodes, or afferent lymphatic conducts, with appropriate formulations and injection devices may induce more efficacious immune responses and protection. In this work, we first reviewed the geographical and functional map of the most important lymphatic elements that play a key role in the induction of a specific immune response, such as site of injection, choice of adjuvants and etc. In a first set of experiments, we demonstrated that short intervals of boosting (daily versus weekly) increase the production of IgG2a antibody against the injected model antigen, while increasing rather than constant booster doses increase the number of antigen-specific CD8(+) IFN-gamma producing cells. Such antigen presentation patterns reflect the initially increasing amounts of antigen associated with natural infections by highly virulent and replicating pathogens. In a second set of experiments, we studied the importance of administration route (subcutaneous, intradermal, intramuscular, intralymphatic) for the induction of antigen-specific IgG2a, and of IFN-gamma produced by antigen-specific lymphocytes when using PLGA microparticles for delivery of antigen. Interestingly, both IgG2a and IFN-gamma production were significantly enhanced after intramuscular and intra-lymph node administration when compared to the other two routes. In conclusion, the results suggest that traditional vaccination schedules and administration routes should be reconsidered in vaccine development, particularly when using more advanced formulations and delivery systems such as micro- and nanoparticles or combinations of antigen and immune-response modifiers