Itay Shomroni

Experimental investigation of the transition between Autler-Townes splitting and electromagnetically-induced transparency models

Summary form only given. If in general the transparency of an initially absorbing medium for a probe field is increased by the presence of a control field on an adjacent transition, two very different processes can be invoked to explain it. One of them is a quantum Fano interference between two paths in the three-level system, which occurs even at low control intensity and gives rise to electromagnetically-induced transparency (EIT), the other one is the appearance of two dressed states in the excited level at higher control intensity, corresponding to the Autler-Townes splitting (ATS). This distinction is particularly critical for instance for the implementation of slow light or optical quantum memories. In a recent paper, P. M. Anisimov, J. P. Dowling and B. C. Sanders proposed a quantitative test to objectively discerning ATS from EIT. We experimentally investigated this test with cold atoms and demonstrated that it is very sensitive to the specific properties of the medium. In this study, we use an ensemble of cold Cesium atoms trapped in a MOT, interacting with light via a Λ-type scheme on the D2 line. Absorption profiles are obtained for various values of the control Rabi frequency Ω between 0.1Γ and 4Γ, where Γ is the natural linewidth.

Weak-values technique for velocity measurements

In a recent Letter, Brunner and Simon proposed an interferometric scheme using imaginary weak values with a frequency-domain analysis to outperform standard interferometry in longitudinal phase shifts [Phys. Rev. Lett105, 010405 (2010)]. Here we demonstrate an interferometric scheme combined with a time-domain analysis to measure longitudinal velocities. The technique employs the near-destructive interference of non-Fourier limited pulses, one Doppler shifted due to a moving mirror in a Michelson interferometer. We achieve a velocity measurement of 400 fm/s and show our estimator to be efficient by reaching its Cramér-Rao bound.

Extraction of a single photon from an optical pulse

A single photon is deterministically extracted from a light pulse due to the interaction of the pulse with a single 87Rb atom coupled to a nanofibre-coupled microresonator. The extraction mechanism is insensitive to pulse shape and timing. Removing a single photon from a pulse is one of the most elementary operations that can be performed on light, having both fundamental significance1,2 and practical applications in quantum communication3,4,5,6,7,8,9 and computation10. So far, photon subtraction, in which the removed photon is detected and therefore irreversibly lost, has been implemented in a probabilistic manner with inherently low success rates using low-reflectivity beam splitters1. Here we demonstrate a scheme for the deterministic extraction of a single photon from an incoming pulse. The removed photon is diverted to a different mode, enabling its use for other purposes, such as a photon number-splitting attack on quantum key distribution protocols11. Our implementation makes use of single-photon Raman interaction (SPRINT)12,13 with a single atom near a nanofibre-coupled microresonator. The single-photon extraction probability in our current realization is limited mostly by linear loss, yet probabilities close to unity should be attainable with realistic experimental parameters13.

Demonstration of weak measurement based on atomic spontaneous emission.

We demonstrate a new type of weak measurement based on the dynamics of spontaneous emission. The pointer in our scheme is given by the Lorentzian distribution characterizing atomic exponential decay via emission of a single photon. We thus introduce weak measurement, so far demonstrated nearly exclusively with laser beams and Gaussian statistics, into the quantum regime of single emitters and single quanta, enabling the exploitation of a wide class of sources that are abundant in nature. We describe a complete analogy between our scheme and weak measurement with conventional Gaussian pointers. Instead of a shift in the mean of a Gaussian distribution, an imaginary weak value is exhibited in our scheme by a significantly slower-than-natural exponential distribution of emitted photons at the postselected polarization, leading to a large shift in their mean arrival time. The dynamics of spontaneous emission offer a broader view of the measurement process than is usually considered within the weak measurement formalism. Our scheme opens the path for the use of atoms and atomlike systems as sensitive probes in weak measurements, one example being optical magnetometry.

Demonstration of fold and cusp catastrophes in an atomic cloud reflected from an optical barrier in the presence of gravity.

We experimentally demonstrate first-order (fold) and second-order (cusp) catastrophes in the density of an atomic cloud reflected from an optical barrier in the presence of gravity and show their corresponding universal asymptotic behavior. These catastrophes, arising from classical dynamics, enable robust, field-free refocusing of an expanding atomic cloud with a wide velocity distribution. Specifically, the density attained at the cusp point in our experiment reached 65% of the peak density of the atoms in the trap prior to their release. We thereby add caustics to the various phenomena with parallels in optics that can be harnessed for manipulation of cold atoms. The structural stability of catastrophes provides inherent robustness against variations in the systems dynamics and initial conditions, making them suitable for manipulation of atoms under imperfect conditions and limited controllability.

Deterministic photon-atom and photon-photon interactions based on single-photon Raman interaction

We demonstrate a passive scheme for deterministic interactions between a single photon and a single atom. Relying on single-photon Raman interaction (SPRINT), this control-fields free scheme swaps a flying qubit, encoded in the two possible input modes of a photon, with a stationary qubit, encoded in the two ground states of the atom, and can be also harnessed to perform universal quantum gates. Using SPRINT we experimentally demonstrated all-optical switching of single photons by single photons, and deterministic extraction of a single photon from an optical pulse. Applicable to any atom-like Lambda system, SPRINT provides a versatile building block for scalable quantum networks based on completely passive nodes interconnected and activated solely by single photons.

Demonstration of Deterministic Photon-Photon Interactions with a Single Atom

We demonstrate all-optical deterministic photon-atom and photon-photon interactions with a single Rb atom coupled to high-Q fiber-coupled microresonator. This scheme enables all-optical photon routing, passive quantum memory and quantum gates activated solely by single photons.

Demonstration of Deterministic Photon-photon Interactions with a Single Atom

We demonstrate deterministic photon-atom and photon-photon interactions with a single atom coupled to a high-Q fiber-coupled microresonator. Based on Deterministic One Photon Raman Interaction (DOPRI), this scheme can form the basis for all-optical quantum information processing.