Tomography by noise

We present an efficient and robust method for the reconstruction of photon number distributions by using solely thermal noise as a probe. The method uses a minimal number of pre-calibrated quantum devices, only one on/off single-photon detector is sufficient. Feasibility of the method is demonstrated by the experimental inference of single-photon, thermal and two-photon states. The method is stable to experimental imperfections and provides a direct, user-friendly quantum diagnostics tool

Continuous Variable Quantum Cryptography - beating the 3 dB loss limit

We demonstrate that secure quantum key distribution systems based on continuous variables implementations can operate beyond the apparent 3 dB loss limit that is implied by the beam splitting attack . The loss limit was established for standard minimum uncertainty states such as coherent states. We show that by an appropriate postselection mechanism we can enter a region where Eve's knowledge falls behind the information shared between Alice and Bob even in the presence of substantial losses.Comment: 4 pages, 2 figure

Sub shot noise phase quadrature measurement of intense light beams

We present a setup to perform sub shot noise measurements of the phase quadrature for intense pulsed light without the use of a separate local oscillator. A Mach--Zehnder interferometer with an unbalanced arm length is used to detect the fluctuations of the phase quadrature at a single side band frequency. Using this setup, the non--separability of a pair of quadrature entangled beams is demonstrated experimentally.Comment: 9 pages, 2 figures, accepted for publication in Optics Letter

Photon temporal modes: a complete framework for quantum information science

Field-orthogonal temporal modes of photonic quantum states provide a new framework for quantum information science (QIS). They intrinsically span a high-dimensional Hilbert space and lend themselves to integration into existing single-mode fiber communication networks. We show that the three main requirements to construct a valid framework for QIS -- the controlled generation of resource states, the targeted and highly efficient manipulation of temporal modes and their efficient detection -- can be fulfilled with current technology. We suggest implementations of diverse QIS applications based on this complete set of building blocks.Comment: 17 pages, 13 figure

Quantum techniques using continuous variables of light

We present schemes for the generation and evaluation of continuous variable entanglement of bright optical beams and give a brief overview of the variety of optical techniques and quantum communication applications on this basis. A new entanglement-based quantum interferometry scheme with bright beams is suggested. The performance of the presented schemes is independent of the relative interference phase which is advantageous for quantum communication applications.Comment: 11 pages, 5 figures; minor correction, accepted versio

Generation of continuous variable Einstein-Podolsky-Rosen entanglement via the Kerr nonlinearity in an optical fiber

We report on the generation of a continuous variable Einstein-Podolsky-Rosen (EPR) entanglement using an optical fiber interferometer. The Kerr nonlinearity in the fiber is exploited for the generation of two independent squeezed beams. These interfere at a beam splitter and EPR entanglement is obtained between the output beams. The correlation of the amplitude (phase) quadratures is measured to be 4.0±0.2 (4.0±0.4)dB below the quantum noise limit. The sum criterion for these squeezing variances 0.80±0.03<2 verifies the nonseparability of the state. The product of the inferred uncertainties for one beam (0.64±0.08) is well below the EPR limit of unity