The broad brush picture of the QUEST collaboration portfolio is described below. The main external collaborations (in different stages of implementation) are with groups led by:
Seamus Davis,Cornell
(local probes, superfluids)
Poul Jessen, UA and
Ivan Deutsch UNM (quantum control and networks)
Paul Kwiat, Illinois
(quantum optics)
Hideo Mabuchi, Caltech
(quantum control and networks)
Mark Raizen, UT Austin
(cold atoms, quantum optics)
In addition to these collaborations, QUEST team members also pursue independent, albeit smaller, projects in the three main QUEST research areas. It is desirable for these projects to have tangible links with the problems driving the larger collaborations.
Several collaborations within the Lab exist, or are being developed. These include research on quantum dots, fast spectroscopy, local probes, and cold atoms. The LANL experimentalists involved include:
Dana Berkeland, P (ion
traps)
Marilyn Hawley, MST
(local probes)
Richard Hughes, P (ion
traps)
Victor Klimov, C
(quantum dots)
Toni Taylor, MST
(control)
Dave Vieira, C (cold
atoms)
Caltech
Caltech has one of the world's leading efforts in quantum optics. A primary focus is the study of open quantum systems using cavity QED. Recent extensions of this research program in Hideo Mabuchi's group include quantum networks, quantum interconnection and feedback, molecular computation, and molecular biophysics.
The main contact with Caltech is at present in the theory of quantum feedback control and theoretical support for the experimental effort, including construction of a dedicated 72 processor cluster at Los Alamos which is aimed at simulating the dynamics of the coupled atom-cavity system including the effects of quantum measurement back-action while an algorithm burned into an FPGA (Field Programmable Gate Array) provides a (hardware) feedback control loop.
We expect to expand the theoretical effort in several directions. We hope to (1) explore the application of ideas from control theory to problems in nonequilibrium quantum dynamics using ideas borrowed from model reduction techniques, (2) apply the ideas of quantum control theory to explore the ultimate limits of precision active measurements such as will be needed in the final versions of the Laser Interferometric Gravitational Wave Observatory (LIGO), and (3) investigate the possibility of forming quantum networks using magnetically trapped atoms inside photonic band-gap materials (with photons serving as information carriers).
Cornell
Precision STM scanning as a local probe of electronic density has been brought to a high degree of sophistication by Seamus Davis' research group. Recent success of STM experiments on unconventional superconductors, such as high-T_c, has provided a proof of principle that one can tunnel into the superconductor and see nontrivial electronic correlations on nanometer scales. Seminal theoretical work in this area has been carried out by T-Division researchers.
New directions appropriate for QUEST include: (1) Recent STM results have led to the proposed notion of a Josephson Tunneling Microscope (JTM), a phase coherent analog of conventional STM tunneling. The idea is to investigate the tunable Josephson current between the superconducting tip and the superconducting surface. There are a number of predictions regarding the properties of the JTM on unconventional superconductors and carrying out experiments using the latest generation of STMs appears feasible: This is an example of applying basic theory to design a new measuring tool. (2) Investigation of intragap impurity states in the pseudogap regime of high-T_c superconductors: There is a prediction of a resonant impurity state in the pseudogap regime of high-temperature superconductors, which can be used to test the nature of the pseudogap state using a powerful, recently developed, low-temperature STM probe. (3) Time domain STM: This is the least developed version of STM and needs to be looked at theoretically.
STM sensing of a (pinned) vortex distribution on a two-dimensional substrate has also been demonstrated at Berkeley. There is a possibility of measuring information relating to spin transport for localized vortices by keeping the STM tip fixed and obtaining a time series of the differential conductance. Analysis of this time series could in principle allow the testing of theoretical predictions for vortex transport (some work in this area has been recently carried out at Los Alamos).
UT Austin
The research program in Mark Raizen's lab uses laser-cooled atoms in time-dependent optical potentials to study a wide range of fundamental problems. The main areas of interest are quantum chaos, atom optics, and quantum transport in optical lattices. Activities are planned in the areas of cold atom interaction with surfaces, BECs in time-dependent potentials, and atomic cooling without the use of cycling transitions using stochastic cooling techniques.
Theoretical work at Los Alamos (in collaboration with Bala Sundaram at CUNY) has already been carried out in some of the above areas. As an example, we will soon have access to experimental data to verify our predictions of enhanced diffusion in the quantum delta-kicked rotor in a parameter regime close to the quantum-classical transition.
As part of the QUEST initiative, we expect to extend our collaboration in three new directions: (1) Theoretical underpinnings of atomic stochastic cooling. Here we will investigate topics such as the build-up of correlations, optimal cooling strategies, ultimate quantum limits to cooling, and `demon' billiards for purposes of cooling (nonequilibrium evaporative cooling in phase space). (2) Quantum transport in time-dependent or spatial many body systems which could be Fermionic or Bosonic. One interesting area we will study will be the dynamics of a kicked Bose condensate. (3) Interaction of atoms (including condensates) and surfaces. Here we wish to investigate the reflection of cold atoms (perhaps condensates) off nano-particles or other structured surfaces with the aim of producing a new tool for the study of surface and sub-surface properties of materials.
UoA/UNM
Trapped neutral atoms offer a very rich system in which to implement and study quantum coherent dynamics. Optical lattices - microscopic traps created by the ac-Stark effect of a set of interfering laser beams - form a particularly flexible environment. Ivan Deutsch (UNM theory) and Poul Jessen (UA experiment) and their students have a worked together to develop and demonstrate a broad range a tools for quantum control of atomic spinor wave packets in this system including: state preparation via laser cooling to the trap's ground state, observation of mesoscopic quantum tunneling in engineered double-well potentials, and quantum state reconstruction. Further possible developments will include detailed studies of decoherence, reservoir engineering, continuous measurement, and feedback control. In addition, the richness of the atom-photon interaction allow for studies of nontrivial nonlinear dynamics, opening the door to new studies of quantum-chaos and classical/quantum correspondence.
We expect to work together to further develop techniques for coherent control in this system, including studies of individual atom vs. ensemble control, the role of continuous measurement in obtaining classically chaotic motion, and the development of feedback control methods.
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| Salman Habib / T-8 / LANL / habib@shiva.lanl.gov / revised February 02 |  |