PubMed Health⌕ Search

Biomedical subjects

Ralf Schützhold

Publications and source records attributed to Ralf Schützhold.

9 recordsLinked to original sources
PubMed2006

Sweeping from the superfluid to the Mott phase in the Bose-Hubbard model.

We study the sweep through the quantum phase transition from the superfluid to the Mott state for the Bose-Hubbard model with a time-dependent tunneling rate J(t). In the experimentally relevant case of exponential decay J(t) proportional variant e -gamma t, an adapted mean-field expansion for large fillings n yields a scaling solution for the fluctuations. This enables us to analytically calculate the evolution of the number and phase variations (on-site) and correlations (off-site) for slow (gamma< >mu) sweeps, where mu is the chemical potential. Finally, we derive the dynamical decay of the off-diagonal long-range order as well as the temporal shrinkage of the superfluid fraction in a persistent ring-current setup.

Journal Article↗
PubMed2006

Detection scheme for acoustic quantum radiation in Bose-Einstein condensates.

Based on doubly detuned Raman transitions between (meta)stable atomic or molecular states and recently developed atom counting techniques, a detection scheme for sound waves in dilute Bose-Einstein condensates is proposed whose accuracy might reach down to the level of a few or even single phonons. This scheme could open up a new range of applications including the experimental observation of quantum radiation phenomena such as the Hawking effect in sonic black-hole analogues or the acoustic analogue of cosmological particle creation.

Journal Article↗
PubMed2006

Signatures of the Unruh effect from electrons accelerated by ultrastrong laser fields.

We calculate the radiation resulting from the Unruh effect for strongly accelerated electrons and show that the photons are created in pairs whose polarizations are perfectly correlated. Apart from the photon statistics, this quantum radiation can further be discriminated from the classical (Larmor) radiation via the different spectral and angular distributions. The signatures of the Unruh effect become significant if the external electromagnetic field accelerating the electrons is not too far below the Schwinger limit and might be observable with future facilities. Finally, the corrections due to the birefringent nature of the QED vacuum at such ultrahigh fields are discussed.

Journal Article↗
PubMed2005

Dynamical zero-temperature phase transitions and cosmic inflation or deflation.

For a rather general class of scenarios, sweeping through a zero-temperature phase transition by means of a time-dependent external parameter entails universal behavior: In the vicinity of the critical point, excitations behave as quantum fields in an expanding or contracting universe. The resulting effects such as the amplification or suppression of quantum fluctuations (due to horizon crossing, freezing, and squeezing) including the induced spectrum can be derived using the curved space-time analogy. The observed similarity entices the question of whether cosmic inflation itself might perhaps have been such a phase transition.

Journal Article↗
PubMed2005

Hawking radiation in an electromagnetic waveguide?

It is demonstrated that the propagation of electromagnetic waves in an appropriately designed waveguide is (for large wavelengths) analogous to that within a curved space-time--such as around a black hole. As electromagnetic radiation (e.g., microwaves) can be controlled, amplified, and detected (with present-day technology) much easier than sound, for example, we propose a setup for the experimental verification of the Hawking effect. Apart from experimentally testing this striking prediction, this would facilitate the investigation of the trans-Planckian problem.

Journal Article↗
PubMed2004

Resonant cavity photon creation via the dynamical Casimir effect.

Motivated by a recent proposal for an experimental verification of the dynamical Casimir effect, the macroscopic electromagnetic field within a perfect cavity containing a thin slab with a time-dependent dielectric permittivity is quantized in terms of the dual potentials. For the resonance case, the number of photons created out of the vacuum due to the dynamical Casimir effect is calculated for both polarizations. It turns out that only TM modes can be excited efficiently.

Journal Article↗
PubMed2002

Small cosmological constant from the QCD trace anomaly?

According to recent astrophysical observations the large scale mean pressure of our present Universe is negative suggesting a positive cosmological constant-like term. The issue of whether nonperturbative effects of self-interacting quantum fields in curved space-times may yield a significant contribution is addressed. Focusing on the trace anomaly of quantum chromodynamics, a preliminary estimate of the expected order of magnitude yields a remarkable coincidence with the empirical data, indicating the potential relevance of this effect.

Journal Article↗
PubMed2002

Dielectric black hole analogs.

As an alternative to the sonic black hole analogs we discuss a different scenario for modeling the Schwarzschild geometry in a laboratory--the dielectric black hole. The dielectric analog of the horizon occurs if the velocity of a medium with a finite permittivity exceeds the speed of light in that medium. The relevance for experimental tests of the Hawking effect and possible implications are addressed.

Journal Article↗