Over my career I've pursued a variety of topics in atomic physics, nonlinear optics, quantum optics, quantum computation, and quantum imaging and communications.  Links to many of my publications can be obtained through my  Google Scholar page.  Some details of my current work can be found on the site for the Quantum Information Processing group (QuIP) at Raytheon BBN Technologies, where I work on a variety of topics in quantum information.   Over my career, I have focused on the following topics:

  • Coherent non-linear optics.  Some of my early work focused on electromagnetically induced transparency, slow light, and coherent optical storage cold-atomic vapors.  These effects enable optical nonlinearities at the level of a few photons, quantum memories, and optical buffering and coherent optical processing.   They have subsequently been explored in room-temperature atomic vapors, solids, optical fibers, photonic bandgap crystals, meta-materials, and quantum dots.  Two applications of particular interest to me have been memories for quantum repeaters and controllable time delay for phased array beam steering.  Recently, I have been exploring these effects for microwave frequency photons in superconducting quantum circuits.  
  • Bose-Einstein condensation (BEC) and cold gases.  BEC is a state of matter in which a large number of identical particles condense into a single quantum state at low temperatures.  It was first acheved in dilute atomic gases in 1995, nearly 70 years after its prediction.  Utilizing slow light techniques, my colleagues and I were able to generate "quantum shock waves" in BECs, which decayed into solitons and, subsequently, into superfluid vortices.  I am particularly interested in the dynamics and collisions of these superfluid excitations.  I have also studied various other topics in cold gases, including stability in optical lattices, use of Laguerre-Gauss beams for cold atom trapping, and velocity resonances of cold atoms.
  • Quantum imaging.  One of the interesting shorter term applications of quantum information lies in mechanisms for quantum effects to enhance imaging systems such as LIDAR.  My colleagues and I were able to show how phase sensitive amplfication (PSA) with nonlinear crystals could compensate for inefficient detection and thus improve spatial resolution, range accuracy, and vibrometry performance.  In parallel, I have been interested in the quantum illumination, in which an entangled photon source can be used to improve target detection in noisy, lossy environments.
  • Superconducting qubits.  Quantum computers, when realized, will be able to perform certain tasks, such as factoring large numbers, exponentially faster than with current computers.  This has huge ramifications for cryptography.  There are several physical systems competing to be the basic "qubits"  in a quantum computer. Superconducting quantum circuits in a CQED architecture are one of the most promising.  With colleagues I have been studying the decoherence mechanisms limiting these qubits, ways to improve coherence times, and novel methods to couple qubits and perform two-qubit logic gates.  Ultimately, we are designing a scalable architeecture for a quantum processor based on CQED superconducting circuits.
  • Photon efficienct communications.  Understanding and acheiving the ultimate photon efficiency for classical optical communications (the "Holevo bound") requires an understanding of both the physical detection process at the quantum level and coding techniques.  I have been designing and analyzing some of the first "joint detection receivers" which perform collective measurements over multiple optical pulses.  These are able to fundamentally improve demodulation error and increase capacity compared with all currently employed systems.  Simultaneously I have been considering the optimal design for pulse sequences (codes) to use in conjunction with these joint detection receivers.