Jun Yan
University of Maryland - College Park

Tuesday, Feb. 14, 2012
102 JFB

Refreshments: 3:30 pm in 219 JFB
Lecture 4:00pm (102 JFB)

Title: Shining Light on Graphene

Abstract:

Graphene is an ultra-thin electronic membrane: one layer of carbon atoms arranged in a “chicken wire” hexagonal lattice. Despite the first electronic experiments being performed only several years ago, this material has kept surprising scientists and technologists with its amazing properties and was featured in the 2010 Nobel Prize in Physics. In this talk I will overview the fundamental properties of graphene and discuss their implications in the state-of-the-art technology. In particular, the electrons in graphene are only very weakly disrupted by the thermal agitation of carbon atoms. This, in combination with its unique quantized interaction with light, makes graphene a promising material for sensitive, fast and broadband photodetectors for astronomy, security, medicine and material research.

Gianluigi Catelani
Yale University

Thursday, Feb. 9, 2012
102 JFB

Refreshments: 3:30 pm in 219 JFB
Lecture 4:00pm (102 JFB)

Title: Quasiparticle Effects in Superconducting Qubits

Abstract:

Superconducting qubits based on Josephson junctions are a promising platform for quantum computation, but their lifetimes are too short to implement error correction schemes. In this talk I will discuss an intrinsic relaxation mechanism limiting the lifetime, which is due to the interaction between the qubit degree of freedom and the quasiparticles tunneling through the junctions. Our theory is valid for both equilibrium and nonequilibrium quasiparticles. We find that the qubit decay rate depends on the magnetic flux controlling the qubit. In addition to the relaxation rate, we predict the shift of the qubit frequency. Aspects of our theory have been successfully tested in recent experiments. It also opens ways to differentiate the quasiparticle-induced relaxation from other relaxation mechanisms.

Maiken Mikkelsen
University of California - Berkeley

Wednesday, Feb. 8, 2012
B-1 JFB

Refreshments: 3:30 pm in 219 JFB
Lecture 4:00pm (B-1 JFB)

Title: Spintronics & Nanophotonics for Quantum Information Science

Abstract:

Individual semiconductor quantum dots are attractive systems for the study of fundamental spin dynamics, light-matter interactions, and quantum information applications. A key ingredient for spin-based quantum information processing is the coherent rotation of a spin-state on timescales much faster than the spin coherence time. To achieve this, off-resonant optical pulses are used to create a large effective magnetic field via the optical Stark effect, allowing the coherent rotation of a single electron spin in a quantum dot through arbitrary angles up to pi radians in 30 ps [1]. Non-destructive time-resolved Kerr rotation is used to directly monitor the electron spin dynamics and in addition serves as a sensitive probe of the local nuclear spin environment [2,3]. These experiments demonstrate the sequential initialization, ultrafast manipulation, and detection of a single electron spin in GaAs quantum dot. One of the next challenges for quantum information applications is the creation of on-chip quantum networks. A step towards this goal is the integration of single emitters with nanophotonic structures. Recent experiments demonstrate efficient coupling of a single CdSe/ZnS quantum dot to a deep-subwavelength waveguide revealing strongly enhanced light-matter interactions [4]. These results represent progress towards the implementation of scalable quantum information processing in the solid state.

[1] J. Berezovsky*, M. H. Mikkelsen*, N. G. Stoltz, L. A. Coldren & D. D. Awschalom, Science 320, 349 (2008)
[2] M. H. Mikkelsen, J. Berezovsky, N. G. Stoltz, L. A. Coldren & D. D. Awschalom, Nature Physics 3, 770 (2007)
[3] J. Berezovsky, M. H. Mikkelsen, O. Gywat, N. G. Stoltz, L. A. Coldren & D. D. Awschalom, Science 314, 1916 (2006)
[4] M. H. Mikkelsen*, N. Pholchai*, P. Kolchin*, J. Oh, M. S. Islam & X. Zhang, in preparation