Research in a broad range of topics in quantum and condensed matter physics is carried out by Professors Miles Blencowe, Walter Lawrence, and Lorenza Viola (theory), and Roberto Onofrio, Alexander Rimberg, and Yeong-Ah Soh.

Theory

Professor Blencowe's current research interests are primarily within the area of mesoscopic physics, with a focus on the dynamics of nano-to-mesoscale quantum electromechanical systems. A fundamental motivation is to understand the transition from quantum to classical physics for non-trivial dynamical systems. Prof. Blencowe has active collaborations with researchers at Cornell University, Technion (Israel), and the University of Nottingham (UK).

Professor Lawrence is exploring practical and foundational aspects of quantum information theory. A current focus is the study of alternative operator bases relevant to quantum tomography, such as mutually unbiased measurements and Pauli operators. These bases are being studied particularly for systems of many qubits and many qutrits, although the comparison to continuous systems raises interesting questions for possible future investigation. In a different direction, we have studied decohering effects of the environment on decaying metastable quantum systems. The ultimate goal of this work is to better understand the evolution of a quantum system in contact with an environment and subject to measurement.

Prof. Viola's current research focuses on various theoretical and phenomenological aspect of quantum information physics. A main goal is the development of strategies for controlling realistic open quantum systems. Special emphasis is devoted to schemes for reliable quantum information processing, including dynamical decoupling techniques, noiseless subsystems, and quantum error correcting codes. Another broad research objective is to elucidate the significance of quantum information theory across different fields of physics, including deepening our understanding of quantum correlations in many-body systems, and pushing back the boundaries of quantum-limited measurements. Prof. Viola has active links with Los Alamos National Laboratory, NIST Boulder, MIT, and Imperial College (UK). More information about Prof. Viola's research is available on her group's web site.

Quantum network for protecting a logical qubit in a noiseless subsystem supported by three physical qubits. A noiseless subsystem relies on the occurrence of symmetries in the error process: these symmetries lead to conserved quantities which, under the appropriate conditions, may be used to construct error-free logical qubits. Here, the applied noise has permutation symmetry. The information is initially stored in qubit 3, whereas qubits 1 and 2 are used as ancillae to effect the encoding and decoding transformations that map the information to the protected degree of freedom, and back. Even if the state of the system as a whole is corrupted by noise, information stored in the noiseless subsystem is recovered in qubit 2 after decoding. This idea was experimentally demonstrated using a liquid-state NMR quantum information processor [Viola et al, Science 293, 2059 (2001)].

Experiment

Prof. Onofrio's current research is focused on macroscopic quantum mechanics, in particular topics at the interface between atomic physics and condensed matter physics. These include superfluidity in dilute degenerate atomic systems, Casimir and Casimir-Polder effects, quantum mechanics of macroscopic and mesoscopic resonators. More information about Prof. Onofrio's research is available on his group's web site.

Left: Dual-species trapping and cooling system for 6Li and 87Rb atoms.	Right: CCD image of 6Li trapped cloud

Prof. Rimberg's research focuses on use of radio-frequency and microwave techniques to investigate the dynamics of electrons in such nanostructures as quantum dots and single-electron transistors. This includes use of real-time detection of electron tunneling to study fundamental issues of quantum mechanics and quantum measurement. Particular areas of investigation include use of spin in semiconductor quantum dots for quantum information processing, study of temporal electronic correlations in nanoscale devices, and investigation of the quantum limits of amplifiers. The group has active collaborations with the University of Wisconsin, NIST Boulder and Bell Laboratories. More information about Prof. Rimberg's research is available on his group's web site.

Left: Conductance versus gate and bias voltage for a superconducting single electron transistor capable of acting as a near-quantum-limited charge detector.	Right: SEM image of a single electron transistor coupled to a double quantum dot in a GaAs/AlGaAs heterostructure.

Prof. Soh's research focuses on the magnetism and electronic transport in novel materials including magnetic oxides, magnetic nanodots, and magnetic multilayers. Physics at the mesoscale and nanoscale is investigated by fabricating nanodevices or by using local probes. The group has active collaborations with University College London, Cambridge, and Argonne National Laboratory.

Recent Publications

M.P. Blencowe and E. Buks, "Quantum analysis of a linear dc SQUID mechanical displacement detector," Phys. Rev. B 76, 014511 (2007).

A. Naik, O. Buu, M.D. LaHaye, A.D. Armour, A.A. Clerk, M.P. Blencowe, and K.C. Schwab,"Cooling a nanomechanical resonator with quantum back-action," Nature 443, 262 (2006).

W.E. Lawrence, "Rotational properties and GHZ contradictions in N-Qubit systems," quant-ph/0506063 (7 June 2005)

W.E. Lawrence, M.N. Wybourne, and S.M. Carr, "Compressional mode softening and Euler buckling patterns in mesoscopic beams," New Journal of Physics 8, 223 (2006).

M. Brown-Hayes, Q. Wei, W.J. Kim, and R. Onofrio, "Development of an Apparatus for Cooling 6Li-87Rb Fermi-Bose Mixtures in a Light-Assisted Magnetic Trap," Laser Physics vol.17, no.4, 514 (2007).

W.J. Kim, J. H. Brownell, R. Onofrio, "Detectability of dissipative motion in quantum vacuum via superradiance," Phys. Rev. Lett. 96, 200402 (2006).

W. Lu, Z. Li, N. Pfeiffer, K.W. West. and A.J. Rimberg, "Real-time detection of electron tunneling in a quantum dot," Nature 423, 422 (2003).

W. Lu, K.D. Maranowski, and A.J. Rimberg, "Superconducting single-electron transistor coupled to a locally tunable electromagnetic environment," Applied Physics Letters 81, 4976 (2002).

"Electrical effects of spin density wave quantization and magnetic domain walls in chromium", Ravi K. Kummamuru and Yeong-Ah Soh, Nature 452, 859 - 863 (2008).

Guangyong Xu, C. Broholm, Yeong-Ah Soh, G. Aeppli, J. F. DiTusa, Yin Cheng, M. Kenzelmann,C. D. Frost, T. Ito, K. Oka, H. Takagi, "Mesoscopic Phase Coherence in a Quantum Spin Fluid," Science 317, 1049 (2007).

R. Blume-Kohout, H. K. Ng, D. Poulin, and L. Viola, "Characterizing the structure of preserved information in quantum processes," Phys. Rev. Lett. 100, 030501 (2008).

S. Boixo, L. Viola, and G. Ortiz, "Generalized coherent states as preferred states of open quantum systems," Europhys. Lett. 79, 40003 (2007).

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