Manipulation and Measurement of Nonclassical States of Light with Atomic Ensembles

DoctorQuantum lights have been the essential sources for exploring fundamental quantum effects in quantum optics and for carrying out novel quantum protocols in quantum computation and quantum communication. Because photons do not interact with each other in free-space, some kinds of mediums for the interac- tion are required for generating the non-classical lights via parametric processes and for storing and trapping the photons. For the coherent light-matter interac- tions, atoms, the natural particles, have been the ideal platform for their natural indistinguishability. In this dissertation, a series of experiments in an atomic ensemble are described where several properties of photons are manipulated and the quantum states of photons are measured. The first part of this dissertation is the manipulation of photons. In chapter II, a coherent and dynamic beam splitter based on light storage in cold atoms is demonstrated. An input weak laser pulse is first stored in a cold atom ensemble via electromagnetically-induced transparency. A set of counter-propagating control fields, applied at a later time, retrieves the stored pulse into two output spatial modes. Furthermore, by manipulating the control lasers, it is possible to dynamically control the storage time, the power splitting ratio, the relative phase, and the optical frequencies of the output pulses. In chapter IV, the devel- opment of an optical quantum memory with a rubidium-87 cold atom ensemble is reported. By increasing the optical depth of the medium, I achieved a storage e ciency of 65% and a coherence time of 51 μs for a weak laser pulse. In chapter V, I demonstrate the trapping of a single photon whose group velocity becomes zero in a cold atomic ensemble, known as the stationary light. A single collective excitation, known as the spinwave, is first heralded via a writhing pulse. Then, the spinwave is retrieved as the photonic excitation by applying the two counter- propagating reading pulses. Due to the interference of these fields, the single photon stationary light is formed in the cold atomic ensemble. The second part of this dissertation is the measurement of photons. In chapter III, stimulated emission tomography of the frequency-time two-photon wavefunction of narrowband entangled photons from cold atoms is demonstrated. Complete characterization of the narrowband entangled photons requires acquir- ing the frequency-time two-photon wavefunction, involving both joint temporal intensity (JTI) and joint temporal phase (JTP) measurements. Over six orders of magnitude improvement in the measurement time for obtaining JTI and JTP is shown comparing to the conventional direct photon counting method, thus paving the way toward ultrafast high-resolution quantum tomography of pho- tonic quantum states