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Search Results: 1 - 10 of 6384 matches for " Ralf Schützhold "
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Recreating Fundamental Effects in the Laboratory?
Ralf Schützhold
Physics , 2010,
Abstract: This article provides a brief (non-exhaustive) overview of some possibilities for recreating fundamental effects which are relevant for black holes (and other gravitational scenarios) in the laboratory. Via suitable condensed matter analogues and other laboratory systems, it might be possible to model the Penrose process (superradiant scattering), the Unruh effect, Hawking radiation, the Eardley instability, black-hole lasers, cosmological particle creation, the Gibbons-Hawking effect, and the Schwinger mechanism. Apart from an experimental verification of these yet unobserved phenomena, the study of these laboratory systems might shed light onto the underlying ideas and problems and should therefore be interesting from a (quantum) gravity point of view as well.
Fundamental Quantum Effects from a Quantum-Optics Perspective
Ralf Schützhold
Physics , 2010,
Abstract: This article provides a brief overview of some fundamental effects of quantum fields under extreme conditions. For the Schwinger mechanism, Hawking radiation, and the Unruh effect, analogies to quantum optics are discussed, which might help to approach to these phenomena from an experimental point of view.
Dynamical quantum phase transitions
Ralf Schützhold
Physics , 2010, DOI: 10.1007/s10909-008-9831-5
Abstract: A sweep through a quantum phase transition by means of a time-dependent external parameter (e.g., pressure) entails non-equilibrium phenomena associated with a break-down of adiabaticity: At the critical point, the energy gap vanishes and the response time diverges (in the thermodynamic limit). Consequently, the external time-dependence inevitably drives the system out of equilibrium, i.e., away from the ground state, if we assume zero temperature initially. In this way, the initial quantum fluctuations can be drastically amplified and may become observable -- especially for symmetry-breaking (restoring) transitions. By means of several examples, possible effects of these amplified quantum fluctuations are studied and universal features (such as freezing) are discussed.
Emergent Horizons in the Laboratory
Ralf Schützhold
Physics , 2010, DOI: 10.1088/0264-9381/25/11/114011
Abstract: The concept of a horizon known from general relativity describes the loss of causal connection and can be applied to non-gravitational scenarios such as out-of-equilibrium condensed-matter systems in the laboratory. This analogy facilitates the identification and theoretical study (e.g., regarding the trans-Planckian problem) and possibly the experimental verification of "exotic" effects known from gravity and cosmology, such as Hawking radiation. Furthermore, it yields a unified description and better understanding of non-equilibrium phenomena in condensed matter systems and their universal features. By means of several examples including general fluid flows, expanding Bose-Einstein condensates, and dynamical quantum phase transitions, the concepts of event, particle, and apparent horizons will be discussed together with the resulting quantum effects.
"Exotic" quantum effects in the laboratory?
Ralf Schützhold
Physics , 2010, DOI: 10.1098/rsta.2008.0093
Abstract: This Article provides a brief (non-exhaustive) review of some recent developments regarding the theoretical and possibly experimental study of "exotic" quantum effects in the laboratory with special emphasis on cosmological particle creation, Hawking radiation, and the Unruh effect.
Quantum back-reaction problems
Ralf Schützhold
Physics , 2007,
Abstract: The macroscopic behavior of many physical systems can be approximately described by classical quantities. However, quantum theory demands the existence of omnipresent quantum fluctuations on top of this classical background -- which, albeit small, should have some impact onto its dynamics. The correct treatment of this quantum back-reaction is one of the main problems in quantum gravity and related to fundamental questions such as the initial (big bang) singularity or the cosmological constant. By means of the qualitative analogy between gravity and fluid dynamics, we try to shed some light onto these problems and show some of the difficulties associated with the calculation of the quantum back-reaction starting from the classical (macroscopic) equation of motion.
On the Particle Definition in the presence of Black Holes
Ralf Schützhold
Physics , 2000, DOI: 10.1103/PhysRevD.63.024014
Abstract: A canonical particle definition via the diagonalisation of the Hamiltonian for a quantum field theory in specific curved space-times is presented. Within the provided approach radial ingoing or outgoing Minkowski particles do not exist. An application of this formalism to the Rindler metric recovers the well-known Unruh effect. For the situation of a black hole the Hamiltonian splits up into two independent parts accounting for the interior and the exterior domain, respectively. It turns out that a reasonable particle definition may be accomplished for the outside region only. The Hamiltonian of the field inside the black hole is unbounded from above and below and hence possesses no ground state. The corresponding equation of motion displays a linear global instability. Possible consequences of this instability are discussed and its relations to the sonic analogues of black holes are addressed. PACS-numbers: 04.70.Dy, 04.62.+v, 10.10.Ef, 03.65.Db.
On the detectability of quantum radiation in Bose-Einstein condensates
Ralf Schützhold
Physics , 2006,
Abstract: 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. PACS: 03.75.Kk, 04.70.Dy, 42.65.Dr.
Pattern recognition on a quantum computer
Ralf Schützhold
Physics , 2002, DOI: 10.1103/PhysRevA.67.062311
Abstract: By means of a simple example it is demonstrated that the task of finding and identifying certain patterns in an otherwise (macroscopically) unstructured picture (data set) can be accomplished efficiently by a quantum computer. Employing the powerful tool of the quantum Fourier transform the proposed quantum algorithm exhibits an exponential speed-up in comparison with its classical counterpart. The digital representation also results in a significantly higher accuracy than the method of optical filtering. PACS: 03.67.Lx, 03.67.-a, 42.30.Sy, 89.70.+c.
Dynamical zero-temperature phase transitions and cosmic inflation/deflation
Ralf Schützhold
Physics , 2005, DOI: 10.1103/PhysRevLett.95.135703
Abstract: 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. PACS: 73.43.Nq, 04.62.+v, 98.80.Cq, 04.80.-y.
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