Groups | Seminars || Courses | Outreach


Seminars will be held held at room S-141 in the Physics and Astronomy Department building on Mondays at 4:00 PM, unless noted otherwise.


Spring 2018

January 22, 2018

Prof. Ting Yu
Stevens Institute of Technology

Non-Markovian Dynamics of Open Quantum Systems: Recent Development

(Host: Jin Wang)

In this talk I will report our recent work on quantum dynamics of open systems coupled to an external environment. We will study the crossover property between non-Markovian and Markov dynamics induced by a hierarchical environment consisting of a cavity-reservoir system. We show how the non-Markovian character of the system of interest is influenced by the coupling strength between the qubit and cavity and the correlation time of the reservoir. In particular, we found a new phenomenon whereby the qubit Markovian and non-Markovian transition exhibits an anomalous pattern in a parameter space depicted by the coupling strength and the correlation time of the reservoir. In addition, I will report some recent developments of quantum trajectory methods for cavity QED systems.

January  25, 2018 (11am, YITP)

Dr. Stephen Libby
Lawrence Livermore Nat'l Laboratory

Cold Atom Sensing, Gravity, Tomography, and Gyroscopes

(Host: George Sterman, YITP)

The ability to use lasers to cool atoms to micro-kelvin temperatures and to subsequently control their quantum mechanical behavior has led to the development of exquisitely precise 'quantum' sensors.2 Applications of these sensors include the measurement of local gravitational anomalies to unprecedented accuracy and very accurate, highly stable gyroscopes. Our LLNL - AOSense, Inc. collaboration is pursuing diverse applications of these sensors that directly exploit their extraordinary scale factor stability, low noise and bias drift characteristics. These applications include shielded threat detection in passing vehicles, emergency response, and treaty verification, all of which require rapid, passive methods to determine hidden mass configurations precisely and/or verify the masses present in containers. Such dense, localized objects can in principle be discovered and accurately measured by their effect on the local gravitational field.   Furthermore, near field measurements of these gravitational perturbations from multiple vantage points allow for a kind of gravitational 'tomography,' leading to the real-time determination of the hidden mass distribution. Additionally, we are interested in the potential of atom interferometer Sagnac gyroscopes to do accurate 'dead reckoning' navigation without the aid of GPS.4 After reviewing the physics of atom interferometry in atomic fountain-Mach-Zehnder and Sagnac configurations, I will describe the development of a 'gravity tomography' signal analysis system for vehicle portals, including the optimal synthesis of the gravitational sensor signals with complementary radiation detection.

February 26, 2018

Prof. Daniel Turner

Spectroscopic Observation of Triplet Separation as a Driving Force of Singlet Fission

(Host: Tom Allison)

Singlet fission, a multistep molecular process in which one photon generates two triplet excitons, holds great technological promise. Here, by applying a combination of transient transmittance and two-dimensional electronic spectroscopy with 5 fs laser pulses, we resolve the full set of fission steps before the onset of spin dephasing. In addition to its role as a viable singlet fission material, single-crystalline rubrene is selected because its energetics and transition dipole alignment uniquely allow for the unambiguous identification of the various fission steps through their contributions to distinct spectroscopic features. The measurements reveal that the neighboring correlated triplet pair achieves its maximum population within 20 fs. Subsequent growth of the triplet signal on picosecond time scales is attributable to spatial separation of the triplets, proceeding nonadiabatically through weakly coupled but near-resonant states. As such, we provide evidence in crystalline rubrene for a singlet fission step that, until now, has not been convincingly observed.

March 5, 2018

Prof. Carlos Trallero
University of Connecticut

An attosecond self-referencing interferometer for phase measurement and control of electronic wavepackets

(Host: Tom Weinacht)

We use an equivalent to the Young double-slit interferometer for attosecond pulses to control and directly measure the phase of electrons in the continuum. We can perform this with a resolution of 12.5 attoseconds (half the atomic unit of time) and with sub-attosecond precision.