Mark C. Booth

Counterpropagating entangled photons from a waveguide with periodic nonlinearity

Quantum Imaging Laboratory, Department of Electrical & Computer Engineering,Boston University, 8 Saint Mary’s Street, Boston, Massachusetts 02215(Dated: February 1, 2008)The conditions required for spontaneous parametric down-conversion in a waveguide with periodicnonlinearity in the presence of an unguided pump field are established. Control of the periodic non-linearity and the physical properties of the waveguide permits the quasi-phase matching equationsthat describe counter-propagating guided signal and idler beams to be satisfied. We compare thetuning curves and spectral properties of such counter-propagating beams to those for co-propagatingbeams under typical experimental conditions. We find that the counter-propagating beams exhibitnarrow bandwidth permitting the generation of quantum states that possess discrete-frequency en-tanglement. Such states may be useful for experiments in quantum optics and technologies thatbenefit from frequency entanglement.

Biphoton focusing for two-photon excitation

We study two-photon excitation using biphotons generated via the process of spontaneous parametric down conversion in a nonlinear crystal. We show that the focusing of these biphotons yields an excitation distribution that is the same as the distribution of one-photon excitation at the pump wavelength. We also demonstrate that biphoton excitation in the image region yields a distribution whose axial width is approximately that of the crystal thickness and whose transverse width is that of the pump at the input to the crystal.

Controllable frequency entanglement via auto-phase-matched spontaneous parametric down-conversion

A new method for generating entangled photons with controllable frequency correlation via spontaneous parametric down-conversion (SPDC) is presented. The method entails initiating counter-propagating SPDC in a single-mode nonlinear waveguide by pumping with a pulsed beam perpendicular to the waveguide.

Polarization-sensitive quantum-optical coherence tomography

We set forth a polarization-sensitive quantum-optical coherence tomography (PS-QOCT) technique that provides axial optical sectioning with polarization-sensitive capabilities. The technique provides a means for determining information about the optical path length between isotropic reflecting surfaces, the relative magnitude of the reflectance from each interface, the birefringence of the interstitial material, and the orientation of the optical axis of the sample. PS-QOCT is immune to sample dispersion and therefore permits measurements to be made at depths greater than those accessible via ordinary optical coherence tomography. We also provide a general Jones matrix theory for analyzing PS-QOCT systems and outline an experimental procedure for carrying out such measurements.

Polarization-sensitive quantum optical coherence tomography: Experiment

Abstract Polarization-sensitive quantum optical coherence tomography (PS-QOCT) makes use of a Type-II twin-photon light source for carrying out optical sectioning with polarization sensitivity. A BBO nonlinear optical crystal pumped by a Ti:sapphire psec-pulsed laser is used to confirm the theoretical underpinnings of this imaging paradigm. PS-QOCT offers even-order dispersion cancellation with simultaneous access to the group-velocity dispersion characteristics of the interstitial medium between the reflecting surfaces of the sample.

Temperature and wavelength dependence of Fermi-tail photoemission and two-photon photoemission from multialkali semiconductors

Two-photon photoemission is a useful technique for examining interface, surface, and image-potential states in various materials. We report the temperature and wavelength dependences of the two-photon photoemission yield for several multialkali semiconductors used as photocathode materials in commercially available photomultiplier tubes. We also report the dependence on temperature and wavelength of one-photon photoemission associated with the Fermi tail of the electron-occupancy probability distribution, which can mask two-photon photoemission. The results are expected to be of use in entangled-photon photoemission experiments, for which a large value of the two-photon photoemission yield is required.

One-way autocompensating quantum cryptography via auto-phase-matched spontaneous parametric down-converstion

We present a new quantum cryptography implementation that uses frequency-correlated photon pairs to combine one-way operation with an autocompensating feature that has hitherto only been available in implementations that require the signal to make a round trip between the users. Furthermore, we describe a new scheme for creating frequency-correlated photon pairs (auto-phase-matched spontaneous parametric down-conversion). The new scheme offers several advantages over previous schemes, including the ability to generate frequency-correlated photon pairs regardless of the dispersion characteristics of the system.

Counterpropagating entangled photons in a periodically poled nonlinear waveguide

Entangled photons, which may be generated through the process of spontaneous parametric down-conversion (SPDC) in a crystal with /spl chi//sup (2)/ nonlinearity, have long been in the spotlight for quantum-optics experiments. The generation of entangled photons by quasi-phase matching (QPM) in lithium niobate offers the promise of increased photon-pair production and, with the integration of a waveguide structure, control of the spatial characteristics of the down-converted photons. It turns out that the use of a waveguide structure, in conjunction with periodic poling to achieve quasi-phase matching, offers another critically important feature: the possibility of generating counterpropagating signal and idler photons. We consider the conditions required for generating counterpropagating photon beams and explore some of the unique properties of this source of light using a periodically poled LiNbO/sub 3/ waveguide.