A team of physicists from Austria has sent pairs of entangled photons, which can be used to encrypt messages with complete security, between telescopes spaced 144km apart in the Canary Islands. The researchers say that preserving entanglement over this distance shows the feasibility of carrying out quantum cryptography using a worldwide network of satellites.

ArXiv identifier: 
0810.4340
Speakers: 
S. Virmani
Authors: 
M. B. Plenio and S. Virmani

We consider the possibility of adding noise to a quantum circuit to make it efficiently simulatable classically. In previous works this approach has been used to derive upper bounds to fault tolerance thresholds - usually by identifying a privileged resource, such as an entangling gate or a non-Clifford operation, and then deriving the noise levels required to make it `unprivileged'. In this work we consider extensions of this approach where noise is added to Clifford gates too, and then `commuted' around until it concentrates on attacking the non-Clifford resource.

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.

Researchers at the National Institute of Standards and Technology (NIST) have proved, for the first time, that the lifetime of quantum-computing bits can be extended. In their experiment, they showed that by applying specially timed magnetic pulses to qubits, made of beryllium ions, they could prolong the life of the quantum bits from about one millisecond to hundreds of milliseconds. The work is described in this week's Nature.