Physical processes that could facilitate coherent control of light propagation are under active exploration. In addition to their fundamental interest, these efforts are stimulated by practical possibilities, such as the development of a quantum memory for photonic states. Controlled localization and storage of photonic pulses may also allow novel approaches to manipulating of light via enhanced nonlinear optical processes. Recently, electromagnetically induced transparency was used to reduce the group velocity of propagating light pulses and to reversibly map propagating light pulses into stationary spin excitations in atomic media. Here we describe and experimentally demonstrate a technique in which light propagating in a medium of Rb atoms is converted into an excitation with localized, stationary electromagnetic energy, which can be held and released after a controllable interval. Our method creates pulses of light with stationary envelopes bound to an atomic spin coherence, offering new possibilities for photon state manipulation and nonlinear optical processes at low light levels.

We demonstrate a fiber-optical switch that is activated at tiny energies corresponding to few hundred optical photons per pulse. This is achieved by simultaneously confining both photons and a small laser-cooled ensemble of atoms inside the microscopic hollow core of a single-mode photoniccrystal fiber and using quantum optical techniques for generating slow light propagation and large nonlinear interaction between light beams.

and † These authors contributed equallyWe study dynamics of the interaction between two weak light beams mediated by a strongly coupled quantum dot-photonic crystal cavity system. First, we perform all optical switching of a weak continuous-wave signal with a pulsed control beam, and then perform switching between two pulsed beams (40ps pulses) at the single photon level. Our results show that the quantum dot-nanocavity system creates strong, controllable interactions at the single photon level.Techniques to efficiently interact single photons with quantum emitters are fundamental to the field of quantum optics and quantum information and are at the core of a range of protocols, including two-qubit phase gates [1,2] and quantum non-demolition measurements [3]. In addition, single-photon-level optical nonlinearities may enable ultra-low power and high-speed all-optical gates and switches for classical optical information processing [4,5]. Recent experiments have shown that the necessary nonlinearity may be realized using atomic gases in the slow light regime [6] or solid-state systems consisting of a single quantum dot (QD) strongly coupled to a nano-cavity [7][8][9]. As a crucial next step in the solid state approach, we describe here the time-resolved dynamics of light interacting the QD-cavity system. We first study the the interaction of a weak continuous-wave signal and a pulsed control, and then the interaction of two short (40 ps) pulses.The experiment is performed using a QD dot strongly coupled to three-hole (L3) photonic crystal (PC) cavity [10], superposed with a grating to increase the emission directionality [11] (see Fig.1(a)). It was fabricated in a 160 nm thick membrane containing a central layer of self-assembled InAs QDs with a density of ∼ 50/µm 2 and an inhomogeneously distributed exciton emission between 925±15 nm.The eigen-frequencies ω ± of the QD-cavity system are:where ω r and ω d are the cavity and QD resonance frequencies, respectively; κ and γ are the cavity field decay rate and QD dipole decay rate; g denotes the coherent * Electronic address: englund@columbia.edu † Electronic address: arkam@stanford.edu interaction strength between the QD; and δ = ω d − ω r is the cavity-QD detuning. The parameters of the emittercavity system used in the experiment are g/2π = 25 GHz, κ/2π = 27 GHz, γ/2π = 0.1 GHz. Therefore, the expression under square root in Eq. 1 is positive for δ = 0, implying that the system is in the strong coupling regime of the cavity quantum electrodynamics (QED). We characterize the system in a confocal microscope setup in a He flow cryostat ( Fig.1(b)). The photoluminescence (PL) scans in Fig.1(c) show the anticrossing between the QD-like states and the cavity-like states as the temperature is raised from 36K to 42 K, giving the polariton energies given by Eq.1. The cavity reflectivity, obtained using a white light source in the cross-polarized configuration shown in Fig.1(b), shows the same mode splitting in Fig.1(d). These spectral measurements yield the system parameter...

We propose an implementation of a source of strongly sub-Poissonian light in a system consisting of a quantum dot coupled to both modes of a lossy bimodal optical cavity. When one mode of the cavity is resonantly driven with coherent light, the system will act as an efficient photon number filter, and the transmitted light will have a strongly sub-Poissonian character. In addition to numerical simulations demonstrating this effect, we present a physical explanation of the underlying mechanism. In particular, we show that the effect results from an interference between the coherent light transmitted through the resonant cavity and the super-Poissonian light generated by photoninduced tunneling. Peculiarly, this effect vanishes in the absence of the cavity loss.

We show that the recently demonstrated technique for generating stationary pulses of light [Nature 426, 638 (2003)] can be extended to localize optical pulses in all three spatial dimensions in a resonant atomic medium. This method can be used to dramatically enhance the nonlinear interaction between weak optical pulses. In particular, we show that an efficient Kerr-like interaction between two pulses can be implemented as a sequence of several purely linear optical processes. The resulting process may enable coherent interactions between single photon pulses.Techniques that could facilitate controlled nonlinear interactions between few-photon light pulses are now actively explored [1]. Although research into fundamental limits of nonlinear optics has been carried out over the last three decades, there is renewed interest in these problems in part due to e.g. potential applications in quantum information science [2]. In general, such interactions between few-photon pulses are difficult to achieve, as they require a combination of large nonlinearity, low photon loss and tight confinement of the light beams [3]. In addition, long atom-photon interaction times are required. Simultaneous implementation of all of these requirements is by now only feasible in the context of cavity QED [4].In this Letter we describe a novel method for achieving nonlinear interaction between weak light pulses. Our method is based on a recently demonstrated technique [5,6] in which light propagating in a medium of Rb atoms was converted into an excitation with localized, stationary electromagnetic energy, which could be held and released after a controllable interval. This is achieved by using Electromagnetically Induced Transparency (EIT) [7] to coherently control the pulse propagation. We show here that this method can be extended to confine stationary pulses in all three spatial dimensions. This, in turn, can be used to strongly enhance the nonlinear interaction between weak pulses of light. Specifically we demonstrate that an efficient Kerr-like interaction between two pulses can be implemented as a sequence of linear optical processes and atomic state manipulations. Coherent, controlled nonlinear processes at optical energies corresponding to a single light quanta appear feasible.Before proceeding, we note that the present work is closely related to recent studies on the resonant enhancement of nonlinear optical phenomena via EIT [8,9,10,11]. The essence of these studies is to utilize steep atomic dispersion associated with narrow EIT resonances. In such a system, a small AC Stark shift associated with a weak off-resonant pulse of signal light, produces a large change in refractive index for a resonant probe pulse. In order to fully take advantage of this process, long interaction times between signal and probe pulses must be ensured. Although the latter can be achieved by reducing the group velocities of two interacting pulses by equal amounts [12], in practice this results only in a modest increase of the nonlinear optical effici...

We describe the loading of laser-cooled rubidium atoms into a single-mode hollow-core photoniccrystal fiber. Inside the fiber, the atoms are confined by a far-detuned optical trap and probed by a weak resonant beam. We describe different loading methods and compare their trade-offs in terms of implementation complexity and atom-loading efficiency. The most efficient procedure results in loading of ∼30,000 rubidium atoms, which creates a medium with optical depth ∼180 inside the fiber. Compared to our earlier study [1] this represents a six-fold increase in maximum achieved optical depth in this system.

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We theoretically analyze the temporal dynamics of strongly coupled quantum-dot-cavity system driven by a resonant laser pulse and observe the signature of Rabi oscillation in the time-resolved response of the system (i.e., in the numerically calculated cavity output). We derive simplified linear and nonlinear semiclassical models that approximate well the system's behavior in the limits of high-and low-power driving pulses and describe the role of quantum coherence in the exact dynamics of the system. Finally, we also present time-resolved transmission measurements showing the dynamics of a quantum-dot-cavity system in the presence of a short laser pulse.