Regime Of Cavity Quantum Electrodynamics Research Articles

Strong-coupling cavity QED using rare-earth-metal-ion dopants in monolithic resonators: What you can do with a weak oscillator

We investigate the possibility of achieving the strong coupling regime of cavity quantum electrodynamics using rare-earth-metal-ions as impurities in monolithic optical resonators. We conclude that due to the weak oscillator strengths of the rare-earth-metals, it may be possible but difficult to reach the regime where the single photon Rabi frequency is large compared to both the cavity and atom decay rates. However, reaching the regime where the saturation photon and atom numbers are less than one should be much more achievable. We show that in this ``bad cavity'' regime, transfer of quantum states and an optical phase shift conditional on the state of the atom is still possible and suggest a method for coherent detection of single dopants.

Controlled cavity QED and single-photon emission using a photonic-crystal waveguide cavity system

We introduce a photonic crystal waveguide-cavity system for controlling single-photon cavity quantum electrodynamics (QED). Exploiting Bloch mode analysis and medium-dependent Green function techniques we demonstrate that the propagation of single photons can be accurately described analytically for integrated periodic waveguides with little more than four unit cells, including an output coupler. We verify our analytical approach by comparing to rigorous numerical calculations for a range of photonic crystal waveguide lengths. The semiconductor-based nanophotonics system allows one to nanoengineer various regimes of cavity QED with unprecedented control. We demonstrate maximum Purcell factors of greater than 500 and on-chip single-photon beta factors of about 80% efficiency. Both weak and strong-coupling regimes are investigated, and the important role of waveguide length on the output emission spectra is shown for vertically emitted emission and output waveguide emission.

Direct observation of correlations between individual photon emission events of a microcavity laser

Lasers are recognized for coherent light emission, the onset of which is reflected in a change in the photon statistics. For many years, attempts have been made to directly measure correlations in the individual photon emission events of semiconductor lasers. Previously, the temporal decay of these correlations below or at the lasing threshold was considerably faster than could be measured with the time resolution provided by the Hanbury Brown/Twiss measurement set-up used. Here we demonstrate a measurement technique using a streak camera that overcomes this limitation and provides a record of the arrival times of individual photons. This allows us to investigate the dynamical evolution of correlations between the individual photon emission events. We apply our studies to micropillar lasers with semiconductor quantum dots as the active material, operating in the regime of cavity quantum electrodynamics. For laser resonators with a low cavity quality factor, Q, a smooth transition from photon bunching to uncorrelated emission with increasing pumping is observed; for high-Q resonators, we see a non-monotonic dependence around the threshold where quantum light emission can occur. We identify regimes of dynamical anti-bunching of photons in agreement with the predictions of a microscopic theory that includes semiconductor-specific effects.

Externally Mode-Matched Cavity Quantum Electrodynamics with Charge-Tunable Quantum Dots

We present coherent reflection spectroscopy on a charge and dc Stark tunable quantum dot embedded in a high-quality and externally mode-matched microcavity. The addition of an exciton to a single-electron-charged quantum dot forms a trion that interacts with the microcavity just below the strong-coupling regime of cavity quantum electrodynamics. Such an integrated, monolithic system is a crucial step towards the implementation of scalable hybrid quantum-information schemes that are based on an efficient interaction between a single photon and a confined electron spin.

Nonlinear dispersive regime of cavity QED: The dressed dephasing model

Systems in the dispersive regime of cavity quantum electrodynamics (QED) are approaching the limits of validity of the dispersive approximation. We present a model which takes into account nonlinear corrections to the dressing of the atom by the field. We find that in the presence of pure dephasing, photons populating the cavity act as a heat bath on the atom, inducing incoherent relaxation and excitation. These effects are shown to reduce the achievable signal-to-noise ratio in cavity QED realizations where the atom is measured indirectly through cavity transmission and in particular in circuit QED.

Comment on “Coupled dynamics of atoms and radiation-pressure-driven interferometers” and “Superstrong coupling regime of cavity quantum electrodynamics”

In two recent articles [D. Meiser and P. Meystre, Phys. Rev. A 73, 033417 (2006); 74, 065801 (2006)], Meiser and Meystre describe the coupled dynamics of a dense gas of atoms and an optical cavity pumped by a laser field. They make two important simplifying assumptions: (i) The gas of atoms forms a regular lattice and can be replaced by a fictitious mirror and (ii) the atoms strive to minimize the dipole potential. We show that the two assumptions are inconsistent: The configuration of atoms minimizing the dipole potential is not a perfect lattice. Assumption (ii) is erroneous, as in the strong coupling regime the dipole force does not arise from the dipole potential. The real steady state, where the dipole forces vanish, is indeed a regular lattice. Furthermore, the bistability predicted by Meiser and Meystre does not occur in this system.

Light force fluctuations in a strongly coupled atom–cavity system

Between mirrors, the density of electromagnetic modes differs from the one in free space. This changes the radiation properties of an atom as well as the light forces acting on an atom. It has profound consequences in the strong-coupling regime of cavity quantum electrodynamics. For a single atom trapped inside the cavity, we investigate the atom–cavity system by scanning the frequency of a probe laser for various atom–cavity detunings. The avoided crossing between atom and cavity resonance is visible in the transmission of the cavity. It is also visible in the loss rate of the atom from the intracavity dipole trap. On the normal-mode resonances, the dominant contribution to the loss rate originates from dipole-force fluctuations which are dramatically enhanced in the cavity. This conclusion is supported by Monte Carlo simulations.

Superstrong coupling regime of cavity quantum electrodynamics

We describe a qualitatively different regime of cavity quantum electrodynamics, the superstrong coupling regime. This regime is characterized by atom-field coupling strengths of the order of the free spectral range of the cavity, resulting in a significant change in the spatial mode functions of the light field. It can be reached in practice for cold atoms trapped in an optical dipole potential inside the resonator. We present a nonperturbative scheme that allows us to calculate the frequencies and linewidths of the modified field modes, thereby providing a good starting point for a quantization of the theory.

Ultra-long-distance interaction between spin qubits

We describe a method for implementing deterministic quantum gates between two spin qubits separated by centimeters. Qubits defined by the singlet and triplet states of two exchange coupled quantum dots have recently been shown to possess long coherence times. When the effective nuclear fields in the two asymmetric quantum dots are different, total spin will no longer be a good quantum number and there will be a large electric dipole coupling between the two qubit states. We show that when such a double-quantum-dot qubit is embedded in a superconducting microstrip cavity, the strong coupling regime of cavity quantum electrodynamics lies within reach. Virtual photons in a common cavity mode could mediate coherent interactions between two distant qubits embedded in the same structure; the range of this two-qubit interaction is determined by the wavelength of the microwave transition.

Hybrid apparatus for Bose-Einstein condensation and cavity quantum electrodynamics: Single atom detection in quantum degenerate gases

We present and characterize an experimental system in which we achieve the integration of an ultrahigh finesse optical cavity with a Bose-Einstein condensate (BEC). The conceptually novel design of the apparatus for the production of BECs features nested vacuum chambers and an in vacuo magnetic transport configuration. It grants large scale spatial access to the BEC for samples and probes via a modular and exchangeable “science platform.” We are able to produce Rb87 condensates of 5×106 atoms and to output couple continuous atom lasers. The cavity is mounted on the science platform on top of a vibration isolation system. The optical cavity works in the strong coupling regime of cavity quantum electrodynamics and serves as a quantum optical detector for single atoms. This system enables us to study atom optics on a single particle level and to further develop the field of quantum atom optics. We describe the technological modules and the operation of the combined BEC cavity apparatus. Its performance is characterized by single atom detection measurements for thermal and quantum degenerate atomic beams. The atom laser provides a fast and controllable supply of atoms coupling with the cavity mode and allows for an efficient study of atom field interactions in the strong coupling regime. Moreover, the high detection efficiency for quantum degenerate atoms distinguishes the cavity as a sensitive and weakly invasive probe for cold atomic clouds.

Determination of the Number of Atoms Trapped in an Optical Cavity

The number of atoms trapped within the mode of an optical cavity is determined in real time by monitoring the transmission of a weak probe beam. Continuous observation of atom number is accomplished in the strong coupling regime of cavity quantum electrodynamics and functions in concert with a cooling scheme for radial atomic motion. The probe transmission exhibits sudden steps from one plateau to the next in response to the time evolution of the intracavity atom number, from N>or=3 to N=2-->1-->0 atoms, with some trapping events lasting over 1 s.

Perturbative corrections to photon coincidence spectroscopy

Photon coincidence spectroscopy isa promising technique for probing thenonlinear regime of cavity quantumelectrodynamics in the optical domain,however its accuracy is mitigated by twofactors: higher-order photon correlations,which contribute to an enhanced pair countrate, and non-simultaneity of emittedphoton pairs from the optical cavity. Weshow that the technique of photoncoincidence spectroscopy is effective inthe presence of these effects if thequantitative predictions are adjusted toinclude non-simultaneity and higher-ordercorrelations.