2,090 research outputs found
Quantum Theory of a Resonant Photonic Crystal
We present a quantum model of two-level atoms localized in a 3D lattice,
based on the Hopfield theory of exciton polaritons. In addition to a
polaritonic gap at the exciton energy, a photonic bandgap opens up at the
Brillouin zone boundary. Upon tuning the lattice period or angle of incidence
to match the photonic gap with the exciton energy, one obtains a combined
polaritonic and photonic gap as a generalization of Rabi splitting. For typical
experimental parameters, the size of the combined gap is on the order of 25
cm^{-1}, up to 10^5 times the detuned gap size. The dispersion curve contains a
branch supporting slow-light modes with vanishing exciton probability density.Comment: 4 pages, 3 figure
Thermometry and Refrigeration in a Two-Component Mott Insulator of Ultracold Atoms
Interesting spin Hamiltonians can be realized with ultracold atoms in a
two-component Mott insulator (2CMI). It was recently demonstrated that the
application of a magnetic field gradient to the 2CMI enables new techniques of
thermometry and adiabatic cooling. Here we present a theoretical description
which provides quantitative analysis of these two new techniques. We show that
adiabatic reduction of the field gradient is capable of cooling below the Curie
or N\'eel temperature of certain spin ordered phases.Comment: 5 pages, 5 figures (v4): Added journal referenc
Spin gradient thermometry for ultracold atoms in optical lattices
We demonstrate spin gradient thermometry, a new general method of measuring
the temperature of ultracold atoms in optical lattices. We realize a mixture of
spins separated by a magnetic field gradient. Measurement of the width of the
transition layer between the two spin domains serves as a new method of
thermometry which is observed to work over a broad range of lattice depths and
temperatures, including in the Mott insulator regime. We demonstrate the
thermometry in a system of ultracold rubidium atoms, and suggest that
interesting spin physics can be realized in this system. The lowest measured
temperature is 1 nK, indicating that the system has reached the quantum regime,
where insulating shells are separated by superfluid layers.Comment: 5 pages, 3 figures, minor edits for clarit
An analytical model for bore-driven run-up
We use a hodograph transformation and a boundary integral method to derive a new analytical solution to the shallow-water equations describing bore-generated run-up on a plane beach. This analytical solution differs from the classical Shen-Meyer runup solution in giving significantly deeper and less asymmetric swash flows, and also by predicting the inception of a secondary bore in both the backwash and the uprush in long surf. We suggest that this solution provides a significantly improved model for flows including swash events and the run-up following breaking tsunamis
Atomic Resonance and Scattering
Contains research objectives and summary of research.U. S. Air Force-Office of Scientific Research (Contract F44620-72-C-0057)National Science Foundation (Grant GP-39061X)Joint Services Electronics Program (Contract DAAB07-71-C-0300
Spin gradient demagnetization cooling of ultracold atoms
A major goal of ultracold atomic physics is quantum simulation of spin
Hamiltonians in optical lattices. Progress towards this goal requires the
attainment of extremely low temperatures. Here we demonstrate a new cooling
method which consists of applying a time-varying magnetic field gradient to a
spin mixture of ultracold atoms. We have used this method to prepare isolated
spin distributions at positive and negative spin temperatures of +/-50
picokelvin. The spin system can also be used to cool other degrees of freedom,
and we have used this coupling to reduce the temperature of an apparently
equilibrated sample of rubidium atoms in a Mott insulating state to 350
picokelvin. These are the lowest temperatures ever measured in any system.Comment: 4 pages, 4 figures; (v4) Shortened, added journal re
Participation And performance In 8.02x Electricity And Magnetism: The First Physics MOOC From MITx
Massive Open Online Courses are an exciting new avenue for instruction and
research, yet they are full of unknowns. In the Spring of 2013, MITx released
its first introductory physics MOOC through the edX platform, generating a
total enrollment of 43,000 students from around the world. We describe the
population of participants in terms of their age, gender, level of education,
and country of origin, highlighting both the diversity of 8.02x enrollees as
well as gender gap and retention. Using three midterm exams and the final as
waypoints, we highlight performance by different demographic subpopulations and
their retention rates. Our work is generally aimed at making a bridge between
available MOOC data and topics associated with the Physics Education Research
community.Comment: 4 pages, 5 figures, Accepted for publication in the Physics Education
Research Conference Proceedings, Portland OR 201
Phase diagram for a Bose-Einstein condensate moving in an optical lattice
The stability of superfluid currents in a system of ultracold bosons was
studied using a moving optical lattice. Superfluid currents in a very weak
lattice become unstable when their momentum exceeds 0.5 recoil momentum.
Superfluidity vanishes already for zero momentum as the lattice deep reaches
the Mott insulator(MI) phase transition. We study the phase diagram for the
disappearance of superfluidity as a function of momentum and lattice depth
between these two limits. Our phase boundary extrapolates to the critical
lattice depth for the superfluid-to-MI transition with 2% precision. When a
one-dimensional gas was loaded into a moving optical lattice a sudden
broadening of the transition between stable and unstable phases was observed.Comment: 4 figure
Imaging the Mott Insulator Shells using Atomic Clock Shifts
Microwave spectroscopy was used to probe the superfluid-Mott Insulator
transition of a Bose-Einstein condensate in a 3D optical lattice. Using density
dependent transition frequency shifts we were able to spectroscopically
distinguish sites with different occupation numbers, and to directly image
sites with occupation number n=1 to n=5 revealing the shell structure of the
Mott Insulator phase. We use this spectroscopy to determine the onsite
interaction and lifetime for individual shells
Atomic Resonance and Scattering
Contains research objectives and summary of research on four projects and reports on one research project.Joint Services Electronics Program (Contract DAAB07-74-C-0630)U. S. Air Force Office of Scientific Research (Contract F44620-72-C-0057)National Science Foundation (Grant GP-39061X1
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