Search

We propose a scheme of interaction-free bidirectional multi-channel all-optical switching in a multi-level coupling system consisting of four-level atoms confined in a cavity and coupled by a free-space control laser. A signal laser field is coupled into the cavity and excites two separate transitions of atoms simultaneously under the collective strong coupling condition. The transmission and reflection of signal fields form bidirectional output channels. A free-space control laser induces destructive quantum interference in the multi-level excitation of an atom–cavity system, which can be used to switch on/off the output signal lights of transmission/reflection channels. There is no direct coupling of control light and signal light through the cavity-confined atoms because the output of signal light is nearly totally suppressed to the opposite direction when control light is present. The proposed all-optical switching scheme can be realized with high switching efficiency, broad bandwidth, and weak light intensity. It may be useful for future devices of optical routing, optical communications, and various quantum logic elements.

We demonstrate a simple technique to lock the frequency of a laser to an atomic transition with a new technique of subnatural linewidth spectroscopy. The coupled rubidium system exhibits an enhanced absorption spectrum of the probe beam with a subnatural linewidth. Compared with other techniques with an additional laser, our scheme only utilizes a single laser, which will be locked. The observed spectroscopic linewidth is down to about 3.5 MHz. The laser frequency fluctuation is about 226 kHz after locking on. The demonstrated scheme offers a convenient and low-cost technique for laser frequency stabilization and related precision measurements.

Dicke state is fundamentally responsible for many intriguing collective behaviors of many-body systems. To experimentally study how a property of multi-particle states scales with the number of particles, it is essential to have the capability of preparing and measuring multi-particle states with scalable and deterministic number of particles. We report the first observation of Dicke states consisting of two to seven atoms in an atomic vapor by using optical two-dimensional coherent spectroscopy. The unique capability to selectively access specific multi-atom Dicke states in atomic vapors can enable new studies of many-body physics in the presence of thermal motion and offer new opportunities to utilize multi-atom Dicke states for quantum information processing.

We investigate the optical bistability behavior of a two-sided cavity quantum electrodynamics system. The nonlinear input–output relation of the atom–cavity system coupled by two input light fields from two ends of the cavity can be controlled by a control light from the free space. Different from the common optical bistability phenomenon in the atom–cavity system, two separate bistability regions are observed. The bistability threshold and hysteresis loop can be well controlled by the control light. Because of field interference, the output light intensity becomes different with varying the relative phase of two incident fields. The output field intensity at the threshold of the first bistability region approaches zero with either increasing the detuning or lowering the intensity of the control light; thus, the perfect photon absorption condition is extended and a broadband near-perfect photon absorber is realized. Furthermore, we show an asymmetrical transmission feature due to field interference.

We study a cavity quantum electrodynamics system in which a cavity mode couples simultaneously with two separate transitions of three-level atoms, and show that three polariton states are created in the coupled cavity-atom system. We report the observation of such polariton states in an experiment with cold Rb atoms confined in a cavity. The experimental results agree with theoretical calculations based on a semiclassical analysis. The three-level cavity-atom system may be used for a variety of fundamental studies and practical applications.

We show that by manipulating quantum interference in a multi-atom cavity quantum electrodynamics (CQED) system, the nonlinear excitation of the cavity-atom polariton can be resonantly enhanced while the linear excitation is suppressed. Under the appropriate conditions, it is possible to selectively enhance or suppress the polariton excitation with two free-pace laser fields. We report on an experiment with cold Rb atoms in an optical cavity and present experimental results that demonstrate such interference control of the CQED excitation and its direct application to studies of all-optical switching and cross-phase modulation of the cavity-transmitted light.

We propose a two-channel cross-phase modulation (XPM) scheme in a multi-atom cavity quantum electrodynamics system consisting of three-level atoms confined in a cavity and coupled by a free-space control laser. A signal laser field is coupled into the cavity, and its transmission through the cavity and reflection from the cavity form two output channels. We show that the free-space control laser induces quantum destructive interference in the normal mode excitation, which can be used to modulate the phase of the output signal light of the reflection channel and the transmission channel. The analytical results and numerical calculations show that large XPM in the coupled cavity–atom system can be realized at low light intensities.

The pluripotency and differentiation states of embryonic stem cells (ESCs) are regulated by a set of core transcription factors, primarily Sox2, Oct4, and Nanog. Although their transcriptional regulation has been studied extensively, the contribution of posttranslational modifications in Sox2, Oct4, and Nanog are poorly understood. Here, using a CRISPR-Cas9 knockout library screen in murine ESCs, we identify the E3 ubiquitin ligase Stub1 as a negative regulator of pluripotency. Manipulation of Stub1 expression in murine ESCs shows that ectopic Stub1 expression significantly reduces the protein half-life of Sox2, Oct4, and Nanog. Mechanistic investigations reveal Stub1 catalyzes the polyubiquitination and 26S proteasomal degradation of Sox2 and Nanog through K48-linked ubiquitin chains and Oct4 via K63 linkage. Stub1 deficiency positively enhances somatic cell reprogramming and delays differentiation, whereas its enforced expression triggers ESC differentiation. The discovery of Stub1 as an integral pluripotency regulator strengthens our understanding of ESC regulation beyond conventional transcriptional control mechanisms.

We analyze backward four-wave mixing in a four-level system exhibiting electromagnetically induced transparency (EIT). We show that EIT suppression of the linear absorption leads to the resonantly enhanced four-wave mixing process and the conversion efficiency near 100% may be achieved in a dense four-level medium with negligible decoherence decay.

We show that electromagnetically induced transparency suppresses nonlinear absorption of all orders in a multilevel atomic system and leads to selective, multiphoton excitation of resonantly coupled atomic states. Under appropriate conditions, higher-order nonlinear absorption becomes dominant and selective steady-state population inversion is created among the resonantly coupled states.

We report experimental studies of electromagnetically induced transparency in Λ-type and ladder-type atomic systems realized in ^87Rb atoms cooled and confined in a magneto-optical trap. Complete transparency is observed in the Λ-type system with a moderate coupling field. Comparison between the two systems reveals that at the line center of a weak probe transition, destructive interference occurs for the Λ-type system, whereas constructive interference occurs for the ladder-type system. We discuss conditions of complete transparency in the Λ-type system that contains hyperfine magnetic sublevels. Our experimental measurements for the two systems agree with theoretical calculations based on simple three-level Λ-type and ladder-type models.

We observed guiding, collimating, focusing, and splitting of a continuous, low-velocity rubidium atomic beam with a blue-detuned dark-hollow laser beam. The low-velocity atomic beam was produced in a magneto-optical trap and was loaded into the dark center of the hollow beam. By overlapping the dark-hollow beam with the atomic beam, the rubidium atoms could be collimated or focused. When the dark-hollow beam intercepted the atomic beam at an angle, two spatially separated rubidium atomic beams were produced, one of which was extracted and guided by the dark-hollow beam.

We analyze nonlinear excitation in a four-level atomic system that exhibits electromagnetically induced transparency induced by a strong coupling laser. We show that, at the line center of the atomic transition, the nondegenerate two-photon excitation in the dressed states can be enhanced by constructive quantum interference in two excitation paths while the linear absorption is inhibited by destructive quantum interference. We report an experimental study of the interference-enhanced two-photon absorption in a multilevel Λ-type rubidium atomic system and compare the measurements with the theoretical calculations.

It is shown that upconversion lasing without population inversion may be realized in a four-level system pumped stepwise by two coherent fields.

We propose a simple atomic-beam collimator consisting of a blue-detuned cylindrical-hollow (doughnut) laser beam. Cold atoms from a magneto-optical trap are loaded into the doughnut beam and guided in the propagation direction of the doughnut beam. The cold atoms experience efficient Sisyphus cooling induced by the doughnut beam and a weak repumping beam and are collimated in the transverse direction. In the longitudinal direction the cold atoms experience small accelerations that are due to the absorption-induced heating of the doughnut beam and the repumping beam. The cooling, heating, and loss mechanisms in this atomic collimator are analyzed. Our study shows that an intense cold atomic beam with a minimum transverse velocity of ∼2 cm s^−1 (a minimum transverse temperature of ∼1.4 μK) and a brightness of approximately 2×10^13 atoms (sr^−1 cm^−2 s^−1) can be obtained from the collimator.

We analyze the optical potential for atom guidance in a dark hollow laser beam and compare it with that generated by the evanescent wave in a micrometer-sized hollow optical fiber. We calculate dependence of the optical potential on various parameters: radial position r, laser–atom detuning Δ, beam power P_0, and propagation distance Z. We experimentally generated a dark hollow laser beam from a hollow optical fiber with a 7-μm hole diameter and obtained a coupling efficiency of ~50% for the LP_01 mode. Our study shows that a dark hollow laser beam can produce an optical potential deep enough to guide cold atoms from a magneto-optical trap.

We report a far-field micro-imaging technique that is used for the observation and discrimination of the mode patterns in a micron-sized hollow optical fiber as well as for the synthetic measurement of the fiber. By using an M-20×microscope objective lens, we obtained images, magnified by a factor of about 460, from the mode patterns at an output end facet of the hollow fiber with relative measurement accuracy better than 3. This method can be used for clear identification of the mode patterns in the hollow fiber and detailed study of the relationship between the excitation conditions and the excited modes in the hollow fiber. Moreover, it is useful for the measurement of the geometrical sizes of the hollow fiber and for testing the coupling efficiencies of the core and cladding modes in their mixed mode pattern. In addition, this method can be also used in the generation of a dark hollow laser beam with 10-m dark-spot size and the measurement of the focused-spot size of a Gaussian laser beam with about 1-m diameter. © 1998 Society of Photo-Optical Instrumentation Engineers.

The electronic absorption spectra of more than 20 crude oils and asphaltenes are examined. The spectral location of the electronic absorption edge varies over a wide range, from the near-infrared for heavy oils and asphaltenes to the near-UV for gas condensates. The functional form of the electronic absorption edge for all crude oils (measured) is characteristic of the “Urbach tail,” a phenomenology which describes electronic absorption edges in wide-ranging materials. The crude oils all show similar Urbach widths, which are significantly larger than those generally found for various materials but are similar to those previously reported for asphaltenes. Monotonically increasing absorption at higher photon energy continues for all crude oils until the spectral region is reached where single-ring aromatics dominate absorption. However, the rate of increasing absorption at higher energies moderates, thereby deviating from the Urbach behavior. Fluorescence emission spectra exhibit small red shifts from the excitation wavelength and small fluorescence peak widths in the Urbach regions of different crude oils, but show large red shifts and large peak widths in spectral regions which deviate from the Urbach behavior. This observation implies that the Urbach spectral region is dominated by lowest-energy electronic absorption of corresponding chromophores. Thus, the Urbach tail gives a direct measure of the population distribution of chromophores in crude oils. Implied population distributions are consistent with thermally activated growth of large chromophores from small ones.

We develop a theoretical framework for calculating the spectrum of resonance fluorescence emitted by two-level atoms that are excited by a strong bichromatic field. The dressed states for the two-level system that is interacting with a fully modulated field are identified, and the spectral features are interpreted in terms of transitions among these dressed states.

We analyze the transient response induced by a resonant, weak probe laser in a three-level V-type system driven by a strong, resonant coupling laser.The Rabi oscillation of the probe transition contains two frequencies determined by the coupling laser, and the ratio of the two-frequency components can be controlled by a time delay between the probe and the coupling laser. In particular, when both lasers are turned on simultaneously, the optical nutation with the frequency approximately equal to the Rabi frequency of the coupling laser is dominant; when the probe laser is turned on well after the steady state is reached for the coupling transition, the Rabi oscillation of the probe transition still occurs, and the oscillatory frequency is approximately equal to half of the Rabi frequency of the coupling laser. When both the probe and the coupling lasers are strong, the mutual interaction of the two fields and the atomic system may revive the optical nutation with each other.

I analyze a scheme that is capable of producing large Kerr nonlinearities on cavity-atom polaritons in a cavity quantum electrodynamics system consisting of multiple three-level atoms confined in a cavity mode. A weak control laser coupled to the atoms from free space induces destructive quantum interference in the polariton excitation of the coupled cavity-atom system and creates large Kerr nonlinearities on the intra-cavity light field. The scheme can be used for optical switching or cross-phase modulation of the cavity-atom polariton at ultralow light levels.

We report an experimental observation of slow light propagation in cold Rb atoms exhibiting cavity electromagnetically induced transparency (EIT). The steep slope of the atomic dispersion manifested by EIT reduces the light group velocity. The cavity filtering and feedback further contribute to the slowdown and delay of the light pulse propagation. A combination of the cavity and the EIT atomic system significantly improves the performance of the slow light propagation. A propagation time delay of ~200 ns was observed in the cavity and Rb EIT system, which is ~70 times greater than the time delay calculated for the light pulse propagation through the same Rb EIT system without the cavity.

We report an experimental demonstration of all-optical switching at ultralow light levels in coherently prepared Rb atoms. A signal light pulse is switched on and off by a control light pulse at different frequencies in a four-level atomic system based on multiphoton interferences. We observed a switching efficiency of 55% with the signal and control light pulses containing ∼20 photons each, corresponding to a control energy density of ∼10^−5 photons per atomic cross section λ^2/(2π).

We report an experimental observation of nonlinear optical gain and loss assisted by electromagnetically induced transparency (EIT) and simultaneous superluminal and subluminal light propagations. Two circular components of a linearly polarized light initiate third-order nonlinear processes in which one circular component is attenuated while the other component is amplified in a three-level EIT system. Near the atomic resonance, the attenuated circular component experiences steep normal dispersion and propagates with a slow group velocity, while the amplified circular component experiences steep anomalous dispersion and propagates with a superluminal group velocity.

We propose and analyze a hyper-Raman scheme for generation of coherent light in a five-level atomic system based on electromagnetically induced transparency (EIT).?We show that EIT suppresses linear and nonlinear photon absorption and enables the hyper-Raman process to proceed through real, near-resonant intermediate states. The scheme greatly enhances hyper-Raman efficiency and may be used for generating short-wavelength radiation at low pump intensities.

We report an experimental observation of third-order nonlinear absorption by quantum interference in ^87Rb atoms cooled and confined in a magneto-optic trap. A coupling laser creates electromagnetically induced transparency (EIT) in a multilevel Rb system in which the third-order nonlinear absorption is enhanced by constructive quantum interference while the linear absorption is inhibited by destructive interference. Our experiment demonstrates the EIT system proposed by Harris Yamamoto [Phys.??Rev.??Lett.??81, 3611 (1998)], which absorbs two photons but not one photon in the dressed-state picture.

The exponential attenuation of electronic absorption in spectral regions removed from the absorption maxima, the “Urbach tail,” has been observed in a variety of materials and has been ascribed to thermal and structural disorder. Here, we report, to our knowledge, the first observation of the Urbach tail in a multicomponent organic system (the asphaltenes) which is due, in part, to the overlapping absorption spectra of the diverse component chromophores within the tail spectral region. The distribution of chromophores produces an unusually large, nonthermal width in the Urbach tail.

Cavity electromagnetically induced transparency (EIT) in a coherently prepared cavity-atom system is manifested as a narrow transmission peak of a weak probe laser coupled into the cavity mode. We show that, with a resonant pump laser coupling the cavity-confined four-level atoms from free space, the narrow transmission peak of the cavity EIT is split into two peaks. The two peaks represent the dressed intracavity dark states and have a frequency separation approximately equal to the Rabi frequency of the free-space pump laser. We experimentally observed the dressed intracavity dark states in cold Rb atoms confined in a cavity, and the experimental results agree with theoretical calculations based on a semiclassical analysis. [ABSTRACT FROM AUTHOR]