Dynamical Casimir Effect Research Articles

MIR: An experiment for the measurement of the dynamical Casimir effect

In this paper we report the status of the experiment MIR (Motion Induced Radiation), aimed at the experimental verification of the dynamical Casimir effect. The stringent theoretical requirements to observe the effect are satisfied in a scheme in which the conductivity of a semiconductor inside a superconducting microwave resonant cavity is varied in time. Free carriers in the semiconductor are periodically excited and recombine at 5 GHz. In this process vacuum and thermal photons are parametrically amplified in a time interval of 200-500 ns.

Squeezing of a quantum flux in a double rf-SQUID system

We investigate the nonstationary boundary effect for a quantum flux in a double rf-SQUID system. In a superconducting ring interrupted by a dc-SQUID (so-called double rf-SQUID), the Josephson potential can be controlled by the magnetic flux through the dc-SQUID ring. This system is equivalent to an anharmonic oscillator with a time-dependent frequency. A rapid change of the magnetic flux in the dc-SQUID leads to the nonadiabatic mixing of the quantum states for a quantum flux in a double rf-SQUID. Therefore, this becomes a circuit analogue of the dynamical Casimir effect in quantum field theory. We perform numerical calculations for the quantum state evolution of the quantum flux within a harmonic approximation, taking account of the nonadiabatic effect. We found that the resulting state distribution has a super-Poissonian character that reflects flux squeezing caused by the Bogoliubov transformation between eigenstates at different times.

Characterization of a low noise microwave receiver for the detection of vacuum photons

In this work we present measurements of the sensitivity of a low noise microwave receiver developed with the aim to detect a feeble quantum electrodynamics effect known as dynamical Casimir effect. We study the performance of the receiver when it is connected to a transmission line ending with an antenna coupled to a resonant microwave cavity. The noise temperature of the receiver is measured with the method of the variable temperature load resistor. The noise generated by the cavity is measured in a similar way. An equivalent input noise of ( 2.0 ± 0.2 ) × 10 - 22 W / Hz is measured at the receiver input. This is equivalent to a sensitivity of approximately 100 photons, well below the expected signal from the quantum vacuum photons.

Dynamical Casimir effect for a swinging cavity

The resonant scalar particle generation for a swinging cavity resonator in the Casimir vacuum is examined. It is shown that the number of particles grows exponentially when the cavity rotates at a specific external frequency.

Dynamical Casimir effect in oscillating media

We show that oscillations of a homogeneous medium with constant material coefficients produce pairs of photons. Classical analysis of an oscillating medium reveals regions of parametric resonance where the electromagnetic waves are exponentially amplified. The quantum counterpart of parametric resonance is an exponentially growing number of photons in the same parameter regions. This process may be viewed as another manifestation of the dynamical Casimir effect. However, in contrast to the standard dynamical Casimir effect, photon production here takes place in the entire volume and is not due to time dependence of the boundary conditions or material constants.

Dynamical Casimir effect for a massless scalar field between two concentric spherical shells

In this work we consider the dynamical Casimir effect for a massless scalar field---under Dirichlet boundary conditions---between two concentric spherical shells. We obtain a general expression for the average number of particle creation, for an arbitrary law of radial motion of the spherical shells, using two distinct methods: by computing the density operator of the system and by calculating the Bogoliubov coefficients. We apply our general expression to breathing modes: when only one of the shells oscillates and when both shells oscillate in or out of phase. Since our results were obtained in the framework of the perturbation theory, under resonant breathing modes they are restricted to a short-time approximation. We also analyze the number of particle production and compare it with the results for the case of plane geometry.

Laser system generating 250-mJ bunches of 5-GHz repetition rate, 12-ps pulses

We report on a high-energy solid-state laser based on a master-oscillator power-amplifier system seeded by a 5-GHz repetition-rate mode-locked oscillator, aimed at the excitation of the dynamic Casimir effect by optically modulating a microwave resonator. Solid-state amplifiers provide up to 250 mJ at 1064 nm in a 500-ns (macro-)pulse envelope containing 12-ps (micro-)pulses, with a macro/micropulse format and energy resembling that of near-infrared free-electron lasers. Efficient second-harmonic conversion allowed synchronous pumping of an optical parametric oscillator, obtaining up to 40 mJ in the range 750-850 nm.

Dynamical Casimir effect for magnons in a spinor Bose-Einstein condensate

Magnon excitation in a spinor Bose-Einstein condensate by a driven magnetic field is shown to have a close analogy with the dynamical Casimir effect. A time-dependent external magnetic field amplifies quantum fluctuations in the magnetic ground state of the condensate, leading to magnetization of the system. The magnetization occurs in a direction perpendicular to the magnetic field breaking the rotation symmetry. This phenomenon is numerically demonstrated and the excited quantum field is shown to be squeezed.

Vacuum effects in a vibrating cavity: Time refraction, dynamical Casimir effect, and effective Unruh acceleration

Two different quantum processes are considered in a perturbed vacuum cavity: time refraction and dynamical Casimir effect. They are shown to be physically equivalent, and are predicted to be unstable, leading to an exponential growth in the number of photons created in the cavity. The concept of an effective Unruh acceleration for these processes is also introduced, in order to make a comparison in terms of radiation efficiency, with the Unruh radiation associated with an accelerated frame in unbounded vacuum.

Optical properties of atomic Mott insulators: From slow light to dynamical Casimir effects

We theoretically study the optical properties of a gas of ultracold, coherently dressed three-level atoms in a Mott insulator phase of an optical lattice. The vacuum state, the band dispersion and the absorption spectrum of the polariton field can be controlled in real time by varying the amplitude and the frequency of the dressing beam. In the weak dressing regime, the system shows unique ultraslow-light propagation properties without absorption. In the presence of a fast time modulation of the dressing amplitude, we predict a significant emission of photon pairs by parametric amplification of the polaritonic zero-point fluctuations. Quantitative considerations on the experimental observability of such a dynamical Casimir effect are presented for the most promising atomic species and level schemes.

The dynamical Casimir effect for two oscillating mirrors in 3D

The generation of photons in a three-dimensional rectangular cavity with two moving boundaries is studied by using the multiple scale analysis (MSA). It is shown that the number of photons are enhanced for the cavity whose walls oscillate symmetrically with respect to the center of the cavity. The non-stationary Casimir effect is also discussed for the cavity which oscillates as a whole.

Electromagnetic radiation by gravitating bodies

Gravitating bodies in motion, regardless of their constitution, always produce electromagnetic radiation in the form of photon pairs. This phenomenon is an analog of the radiation caused by the motion of dielectric (or magnetic) bodies. It is a member of a wide class of phenomena named dynamical Casimir effects, and it may be viewed as the squeezing of the electromagnetic vacuum. Production of photon pairs is a purely quantum-mechanical effect. Unfortunately, as we show, the emitted radiation is extremely weak as compared to radiation produced by other mechanisms.

Detection of casimir photons with electrons

We propose a method for the detection of a dynamical Casimir effect. Assuming that the Casimir photons are being generated in an electromagnetic cavity with a vibrating wall (dynamical Casimir effect), we consider electrons passing through the cavity to be interacting with the intracavity field. We show that the dynamical Casimir effect can be observed via the measurement of the change in the average or in the variance of the electron’s kinetic energy. We point out that the enhancement of the effect due to finite temperatures makes it easier to detect the Casimir photons.

Dynamical Casimir effect with semi-transparent mirrors, and cosmology**Talk given in the Workshop ‘Quantum Field Theory under the Influence of External Conditions (QFEXT07)’, Leipzig (Germany), September 17–21, 2007.

After reviewing some essential features of the Casimir effect and, specifically, of its regularization by zeta function and Hadamard methods, we consider the dynamical Casimir effect (or Fulling–Davies theory), where related regularization problems appear, with a view to an experimental verification of this theory. We finish with a discussion of the possible contribution of vacuum fluctuations to dark energy, in a Casimir-like fashion, that might involve the dynamical version.

MIR status report: an experiment for the measurement of the dynamical Casimir effect

In this paper, the status of the experiment MIR (motion induced radiation) is reported. This experiment aims at measuring for the first time the dynamical Casimir effect by using an effective motion of a wall of a superconducting microwave resonant cavity. Effective motion is produced by periodic illumination of a semiconductor slab by means of an ultra-high-frequency amplitude modulated laser.

Nonstationary boundary effect for a quantum flux in superconducting nanocircuits

We investigate nonstationary boundary effect for a quantum flux in superconducting quantum nanocircuits. This is a circuit analogue of the dynamical Casimir effect in quantum field theory. We describe a scheme for producing rapidly movable (non-material) boundaries introduced by time-dependent potential and for detecting photons out of the vacuum in the circuit. We also discuss an experimental feasibility of our approach.

Modelling superradiant amplification of Casimir photons in very low dissipation cavities

Recent advances in nanotechnology and atomic physics may allow for a demonstration of the dynamical Casimir effect. An array of film bulk acoustic resonators (FBARs) coherently driven at twice the resonant frequency of a high-quality electromagnetic cavity can generate a stationary state of Casimir photons. These are detected using an alkali atom beam prepared in an inverted population of hyperfine states, with an induced superradiant burst producing a detectable radio-frequency signal. We describe here the results of the simulations of the dynamics of superradiance and superfluorescence, with the aim to optimize the parameters for the detectability of Casimir photons. When the superradiant lifetime is shorter than the dissipation time, we find superradiant evolution to be similar in character but dramatically slower than in the usual lossy case.

Black hole collapse simulated by vacuum fluctuations with a moving semitransparent mirror

Creation of scalar massless particles in two-dimensional Minkowski space-time---as predicted by the dynamical Casimir effect---is studied for the case of a semitransparent mirror initially at rest, then accelerating for some finite time, along a trajectory that simulates a black hole collapse (defined by Walker and Carlitz and Willey), and finally moving with constant velocity. When the reflection and transmission coefficients are those in the model proposed by Barton, Calogeracos, and Nicolaevici [$r(\ensuremath{\omega})=\ensuremath{-}i\ensuremath{\alpha}/(\ensuremath{\omega}+i\ensuremath{\alpha})$ and $s(\ensuremath{\omega})=\ensuremath{\omega}/(\ensuremath{\omega}+i\ensuremath{\alpha})$, with $\ensuremath{\alpha}\ensuremath{\ge}0$], the Bogoliubov coefficients on the backside of the mirror can be computed exactly. This allows us to prove that, when $\ensuremath{\alpha}$ is very large (as in the case of an ideal, perfectly reflecting mirror) a thermal emission of scalar massless particles obeying Bose-Einstein statistics is radiated from the mirror (a blackbody radiation), in accordance with results previously obtained in the literature. However, when $\ensuremath{\alpha}$ is finite (semitransparent mirror, a physically realistic situation) the striking result is obtained that the thermal emission of scalar massless particles obeys Fermi-Dirac statistics. We also show here that the reverse change of statistics takes place in a bidimensional fermionic model for massless particles, namely, that the Fermi-Dirac statistics for the completely reflecting situation will turn into the Bose-Einstein statistics for a partially reflecting, physical mirror.

Theory of the dynamical Casimir effect in nonideal cavities with time-dependent parameters

This is a brief review of the recent progress in the theory of dynamical (non-stationary) Casimir effect in non-ideal cavities and of existing proposals to observe this effect in a laboratory, with an emphasis on the experiment which is under preparation in the University of Padua. The main idea of this experiment is to simulate periodical displacements of the cavity wall by periodical strong changes of conductivity of a thin semiconductor slab illuminated by picosecond laser pulses. In this connection the theory of quantum damped oscillator with arbitrary time dependence of the frequency and damping coefficient has been developed in order to take into account intrinsic losses in the semiconductor slab due to a finite conductivity during the intermediate part of the excitation-recombination cycle. The influence of different parameters, such as the diffusion and mobility coefficients of carriers, surface recombination velocity, absorption coefficient of laser radiation, thickness of the slab and geometry of the cavity, is analysed. Analytical and numerical evaluations show that under realistic experimental conditions, several thousand of quanta of EM field (‘Casimir photons’) could be produced from the initial vacuum state in a high-quality cavity at the lowest resonance frequency 2.5 GHz.

Dynamical Casimir effect for gravitons in bouncing braneworlds

We consider a two-brane system in five-dimensional anti--de Sitter space-time. We study particle creation due to the motion of the physical brane which first approaches the second static brane (contraction) and then recedes from it (expansion). The spectrum and the energy density of the generated gravitons are calculated. We show that the massless gravitons have a blue spectrum and that their energy density satisfies the nucleosynthesis bound with very mild constraints on the parameters. We also show that the Kaluza-Klein modes cannot provide the dark matter in an anti--de Sitter braneworld. However, for natural choices of parameters, backreaction from the Kaluza-Klein gravitons may well become important. The main findings of this work have been published in the form of a Letter [R. Durrer and M. Ruser, Phys. Rev. Lett. 99, 071601 (2007)].