We investigate the interaction between nonclassical light with a tunable multiphoton component and a highly nonlinear medium based on cold Rydberg atoms. The nonclassical field emitted by a DLCZ quantum memory is stored using Rydberg electromagnetically induced transparency, experiencing strong nonlinear response due to the dipole blockade. We show that the storage efficiency in the Rydberg ensemble decreases as a function of the multiphoton strength of the input field, as a result of the nonlinearity. We also show that the autocorrelation function g^{(2)}(0) of the retrieved field after storage in the Rydberg state is considerably reduced, leading to the first demonstration of single photon filtering with nonclassical input light. Finally, we develop a simple simulation that allows us to model the effect of our medium on the input state. This work is a step towards matter-mediated photon-photon interactions with nonclassical light.
Epitaxially grown quantum dots (QDs) are promising sources of nonclassical states of light such as single photons and entangled photons. However, in order for them to be used as a resource for long-distance quantum communication, distributed quantum computation, or linear optics quantum computing, these photons must be coupled efficiently to long-lived quantum memories as part of a quantum repeater network. Here, we theoretically examine the prospects for efficient storage and retrieval of a QD-generated single photon with a 1-ns lifetime in a multilevel atomic system. We calculate using an experimentally demonstrated optical depth of 150 that the storage (total) efficiency can exceed 46
(28
) in a dense, ultracold ensemble of
87Rb atoms. Furthermore, we find that the optimal control pulse required for storage and retrieval can be obtained using a diode laser and an electro-optic modulator rather than a mode-locked, pulsed laser source. Increasing the optical depth, for example, by using Bose-condensed ensembles or an optical cavity, can increase the efficiencies to near unity. Aside from enabling a high-speed quantum network based on QDs, such an efficient optical interface between an atomic ensemble and a QD can also lead to entanglement between collective spin-wave excitations of atoms and the spin of an electron or hole confined in the QD.
A reversible quantum memory allowing us to store and retrieve quantum information serves as a key necessity for implementing many of novel quantum information protocols. As light serves as a reliable long-range carrier of quantum information, and atoms offer the possibility of long storage times, current attempts at creating quantum memories focus on the transfer of the quantum fluctuations of light onto atomic coherences. The work in this thesis focuses on the development of a quantum memory for squeezed light using an ensemble of cold Cesium atoms stored in a magneto-optical trap. Our two major milestones were the development of a source of nonclassical light, and the development of a suitable atomic medium for storage. We first present the results of our efforts to generate a source of squeezed vacuum states resonant with the Cesium D2 line using a PPKTP nonlinear crystal inside of an optical parametric oscillator. Additionally, we characterize these squeezed states by carrying out a quantum state tomography using an iterative maximum likelihood approach. Next we look at the development of a new experiment which would allow us to use cold Cesium atoms as a storage medium in our recently developed magneto-optical trap. As this requires an array of novel tools and experimental techniques, we will discuss the development of these elements, and how they have furthered our progress towards storing quantum states onto our Cesium atoms, and eventually entangling two atomic ensembles.