Featured Video Abstract

ArXiv identifier: 
0901.4470
Speakers: 
Susana F. Huelga
Authors: 
Neil P. Oxtoby, Ángel Rivas, Susana F. Huelga, and Rosario Fazio

We consider non-interacting multi-qubit systems as controllable probes of an environment of defects/impurities modelled as a composite spin-boson environment. The spin-boson environment consists of a small number of quantum-coherent two-level fluctuators (TLFs) damped by independent bosonic baths. A master equation of the Lindblad form is derived for the probe-plus-TLF system.

ArXiv identifier: 
0812.4305
Speakers: 
R. F. Werner
Authors: 
V. B. Scholz and R. F. Werner

The situation of two independent observers conducting measurements on a joint quantum system is usually modelled using a Hilbert space of tensor product form, each factor associated to one observer. Correspondingly, the operators describing the observables are then acting non-trivially only on one of the tensor factors. However, the same situation can also be modelled by just using one joint Hilbert space, and requiring that all operators associated to different observers commute, i.e. are jointly measurable without causing disturbance.

ArXiv identifier: 
0901.4454
Speakers: 
Martin Plenio
Authors: 
Filippo Caruso, Alex W. Chin, Animesh Datta, Susana F. Huelga, Martin B. Plenio

Transport of excitations through networked systems plays an important role in many areas of physics, chemistry, and biology. The uncontrollable interaction of the transmission network with a noisy environment is usually assumed to deteriorate its transport capacity, especially so when the system is fundamentally quantum mechanical. Here we identify key mechanisms through which dephasing noise, contrary to expectation, may actually aid transport through a dissipative network.

ArXiv identifier: 
arXiv:0901.4529
Speakers: 
Adolfo del Campo
Authors: 
Marisa Pons, Adolfo del Campo, J. Gonzalo Muga, Mark G. Raizen

We describe the preparation of atom-number states with strongly interacting bosons in one dimension, or spin-polarized fermions. The procedure is based on a combination of weakening and squeezing of the trapping potential. For the resulting state, the full atom number distribution is obtained. Starting with an unknown number of particles $N_i$, we optimize the sudden change in the trapping potential which leads to the Fock state of $N_f$ particles in the final trap. Non-zero temperature effects as well as different smooth trapping potentials are analyzed.

ArXiv identifier: 
0903.0612
Speakers: 
Daniel Burgarth
Authors: 
Daniel Burgarth, Koji Maruyama

Identifying the nature of interactions in a quantum system is essential in understanding any physical phenomena. Acquiring information on the Hamiltonian can be a tough challenge in many-body systems because it generally requires access to all parts of the system. We show that if the coupling topology is known, the Hamiltonian identification is indeed possible indirectly even though only a small gateway to the system is used. Surprisingly, even a degenerate Hamiltonian can be estimated by applying an extra field to the gateway.

ArXiv identifier: 
0807.2444
Speakers: 
Alvaro Feito Boirac
Authors: 
J.S. Lundeen, A. Feito, H. Coldenstrodt-Ronge, K.L. Pregnell, Ch. Silberhorn, T.C. Ralph, J. Eisert, M.B. Plenio, I.A. Walmsley

Measurement connects the world of quantum phenomena to the world of classical events. It plays both a passive role, observing quantum systems, and an active one, preparing quantum states and controlling them. Surprisingly - in the light of the central status of measurement in quantum mechanics - there is no general recipe for designing a detector that measures a given observable. Compounding this, the characterization of existing detectors is typically based on partial calibrations or elaborate models. Thus, experimental specification (i.e.