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Physical Review Letters

Collective Absorption of Blackbody Radiation by Rydberg Atoms in a Cavity: An Experiment on Bose Statistics and Brownian Motion

J. M. Raimond, P. Goy, M. Groß, Claude Fabre, S. Haroche

Published Jul 12, 1982• 158 citations
Publisher

Abstract

Absorption of blackbody radiation by Rydberg atoms in a resonant cavity is shown to be a collective process in which the atoms behave as a Bose gas. The equilibrium energy of this gas was measured and found equal to twice the photon energy (factor of 2 accounting for atomic transition degeneracy). It is shown that this experiment exhibits the Brownian motion of the atomic-system Bloch vector.

DOI
10.1103/physrevlett.49.117

Related papers

RYDBERG ATOMS AND RADIATION IN A RESONANT CAVITY I, THEORY

S. Haroche, Claude Fabre, J. M. Raimond +3 more

We analyze in this paper various aspects of the interaction of Rydberg atoms with resonant electromagnetic cavity. We show that an ensemble of Rydberg atoms coupled to a single field mode at a finite temperature behaves as a single quantum object exhibiting features of Bose-Einstein statistics and Brownian motion. We analyze the transient amplification of the blackbody field by a Rydberg sample and study the change of the photon emission statistics as a function of time. We also show that an isolated Rydberg atom in a cavity undergoes either an oscillating or a damped evolution according to the respective values of the atom to field coupling and cavity damping times and we analyze this effect in term of a modification of the vacuum field modes surrounding the atom. Experiments to check these effects are under progress and will be described in next paper.

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arXiv:2009.12860•New Journal of Physics•Jul 12, 2021•21 citations
Absorption of blackbody radiation by Rydberg atoms in a resonant cavity is shown to be a collective process in which the atoms behave as a Bose gas. The equilibrium energy of this gas was measured and found equal to twice the photon energy (factor of 2 accounting for atomic transition degeneracy). It is shown that this experiment exhibits the Brownian motion of the atomic-system Bloch vector.
We analyze in this paper various aspects of the interaction of Rydberg atoms with resonant electromagnetic cavity. We show that an ensemble of Rydberg atoms coupled to a single field mode at a finite temperature behaves as a single quantum object exhibiting features of Bose-Einstein statistics and Brownian motion. We analyze the transient amplification of the blackbody field by a Rydberg sample and study the change of the photon emission statistics as a function of time. We also show that an isolated Rydberg atom in a cavity undergoes either an oscillating or a damped evolution according to the respective values of the atom to field coupling and cavity damping times and we analyze this effect in term of a modification of the vacuum field modes surrounding the atom. Experiments to check these effects are under progress and will be described in next paper.
We present various experiments involving Rydberg atoms interacting with resonant microwave electromagnetic fields inside a cavity, allowing to check different features of the theory presented in the previous paper. We first describe experiments about superradiant emission by Rydberg states in the cavity, also called transient Rydberg atoms maser ; the evolution of the system is detected either on the populations by selective field ionization technique or on the microwave field itself by heterodyne detection. Very low thresholds, down to 100 atoms, for the maser emission have been observed. We then describe various aspects of collective absorption of radiation by very excited atoms including the observation of Rabi nutation in a small applied resonant field, the study of the quantum efficiency of this set-up considered as a microwave photon counter, and finally the unexpected characteristics of the blackbody radiation absorption in the cavity.
Rydberg atoms excited in microwave resonators are ideal systems to test quantum electrodynamics on an unusual scale.1 Owing to their very large electric dipole sizes, these atoms are indeed coupled so strongly to infrared and millimeter-wave radiation that the field of a few photons—ultimately the one of a single photon—stored in a cavity is large enough to induce important transition rates during the atomic time of flight across the cavity. As a result quantum radiative effects are observed in a range of frequencies where usual atomic systems behave as purely classical radiators. The enhancement of the spontaneous emission rate of a single atom prepared in a tuned cavity has already been observed.2 For a resonant cavity with very small losses, a point should be reached where the atom can no longer decay but instead reversibly oscillates between the two states involved in the transition resonant with the cavity mode. Experiments aimed at the observation of this new regime of quantum electrodynamics evolution are under way
We study the dynamics of a system composed of two coupled cavities, each interacting with a single Rydberg atom. The interplay between Rydberg-Rydberg interaction and photon hopping enables the transition of the atoms from the collective ground state to the double Rydberg excitation state by individually interacting with the optical normal modes and suppressing the upconversion process between them. The atomic transition is accompanied by the two-photon absorption and emission of the normal modes. Since the energy level structure of the atom-cavity system is photon number dependent there is only a pair of states being in the two-photon resonance. Therefore, the system can act as a quantum nonlinear absorption filter through the nonclassical quantum process, converting coherent light field into a nonclassical state. Meanwhile, the vacuum field in the cavity inspires the Rydberg atoms to simultaneously emit two photons into the normal mode, resulting in obvious emission enhancement of the mode.
Precision measurements of quantum systems often seek to probe or must account for the interaction with blackbody radiation. Over the past several decades, much attention has been given to ac Stark shifts and stimulated state transfer. For a blackbody in thermodynamic equilibrium, these two effects are determined by the expectation value of photon number in each mode of the Planck spectrum. Here we explore how the photon number variance of an equilibrium blackbody generally leads to a parametric broadening of the energy levels of quantum systems that is inversely proportional to the square root of the blackbody volume. We consider the effect in two cases which are potentially highly sensitive to this broadening: Rydberg atoms and atomic clocks. We find that even in blackbody volumes as small as 1 cm3{\mathrm{cm}}^{3}cm3, this effect is unlikely to contribute meaningfully to transition linewidths.
Abstract An ensemble of excited atoms can synchronize emission of light collectively in a process known as superradiance when its characteristic size is smaller than the wavelength of emitted photons. The underlying superradiance depends strongly on electromagnetic (photon) fields surrounding the atomic ensemble. High mode densities of microwave photons from 300 K blackbody radiation (BBR) significantly enhance decay rates of Rydberg states to neighbouring states, enabling superradiance that is not possible with bare vacuum induced spontaneous decay. Here we report observations of the superradiance of ultracold Rydberg atoms embedded in a bath of room-temperature photons. The temporal evolution of the Rydberg | nD ⟩ to |( n + 1) P ⟩ superradiant decay of Cs atoms ( n the principal quantum number) is measured directly in free space. Theoretical simulations confirm the BBR enhanced superradiance in large Rydberg ensembles. We demonstrate that the van der Waals interactions between Rydberg atoms change the superradiant dynamics and modify the scaling of the superradiance. In the presence of static electric fields, we find that the superradiance becomes slow, potentially due to many-body interaction induced dephasing. Our study provides insights into many-body dynamics of interacting atoms coupled to thermal BBR, and might open a route to the design of blackbody thermometry at microwave frequencies via collective, dissipative photon-atom interactions.