TY  - JOUR
A1  - Hoffmann, H.
A1  - Boström, Kim
A1  - Felbinger, Timo
T1  - Comment on Secure direct communication with a quantum one-time pad
N2  - In the paper [Phys. Rev. A 69, 052319 (2004)], a quantum direct communication protocol is proposed which is claimed to be unconditionally secure even for the case of a noisy channel. We show that this is not the case by giving an undetectable attack scheme
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Boström, Kim
A1  - Felbinger, Timo
T1  - Lossless quantum data compression and variable-length coding
N2  - In order to compress quantum messages without loss of information it is necessary to allow the length of the encoded messages to vary. We develop a general framework for variable-length quantum messages in close analogy to the classecal case and show that lossless compression is only possible if the message to be compressed is known to the sender. The lossless compression of an ensemble of messages is bounded from below by its von-Neumann entropy. We show that it is possible to reduce the number of qbits passing through a quantum channel even below the von-Neumann entropy by adding a classical side-channel. We give an explicit communication protocol that realizes lossless and instantaneous quantum data compression. This protocol can be used for both online quatum communication and storage of quantum data.
Y1  - 2002
ER  - 
TY  - JOUR
A1  - Felbinger, Timo
A1  - Schiller, Stephan
A1  - Mlynek, Jürgen
T1  - Oscillation and generation of nonclassical states in three-photon down conversion
N2  - The process of 3-photon down conversion 3 omega -> omega + omega + omega in an optical cavity is analyzed theoretically. A classical feature of this system is a first-order transition of the fundamental mode above a threshold 3omega pump power. We calculate the quantum properties of the steady state both using quantum trajectory simulations, and by perturbation expansion of the density operator. A nongaussian Wigner function exhibiting a threefold symmetry is found. Above threshold the Wigner function displays separate peaks among which tunneling occurs.
Y1  - 1998
ER  - 
TY  - JOUR
A1  - Felbinger, Timo
A1  - Santos, L.
A1  - Wilkens, Martin
A1  - Lewenstein, Maciej
T1  - Time Correlations of a laser-induced Bose-Einstein condensate
N2  - We analyze the multi-time correlations of a laser-induced Bose Einstein condensate. We use quantum stochastic methods to obtain under certain circumstances a Fokker-Planck equation which describes the phase-difussion process, and obtain an analytical expression of the two-time correlations. We perform also quantum Monte Carlo numerical simulations of the correlations, which are in good agreement with the predicted analytical results.
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Eisert, Jens
A1  - Felbinger, Timo
A1  - Papadopolous, P.
A1  - Plenio, M. B.
A1  - Wilkens, Martin
T1  - Classical information and distillable entanglement
N2  - We establish a quantitative connection between the amount of lost classical information about a quantum state and the concomitant loss of entanglement. Using menthods that have been developed for the optimal purification of miced states, we find a class of miced states with known distillable entanglement. These results can be used to determine the quantum capacity of a quantum channel which randomizes the order of transmitted signals.
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Felbinger, Timo
A1  - Wilkens, Martin
T1  - Stochastic Wave-function Simulation of Two-time Correlation Functions
N2  - We propose an algorithm for the numerical simulation of two-time correlation functions by means of stochastic wave function. As a first application, we investigate the two-time correlation function of a nonlinear optical parametric oscillator.
Y1  - 1999
ER  -