With the emergence of an information society, the idea of protecting sensitive data is steadily gaining importance. Conventional encryption methods may not be sufficient to guarantee data protection in the future. Quantum key distribution (QKD) is an emerging technology that exploits fundamental physical properties to guarantee perfect security in theory. However, it is not easy to ensure in practice that the implementations of QKD systems are exactly in line with the theoretical specifications. Such theory-practice deviations can open loopholes and compromise security. Several such loopholes have been discovered and investigated in the last decade. These activities have motivated the proposal and implementation of appropriate countermeasures, thereby preventing future attacks and enhancing the practical security of QKD. This article introduces the so-called field of quantum hacking by summarising a variety of attacks and their prevention mechanisms.
Frequency tuning of single photons from a whispering-gallery mode
resonator to MHz-wide transitions
G. Schunk,
U. Vogl,
F. Sedlmeir,
D. V. Strekalov,
A. Otterpohl,
V. Averchenko,
H. G. L. Schwefel,
G. Leuchs,
Ch. Marquardt
Efficient microwave to optical photon conversion: an electro-optical
realization
Alfredo Rueda,
Florian Sedlmeir,
Michele C. Collodo,
Ulrich Vogl,
Birgit Stiller,
Gerhard Schunk,
Dmitry V. Strekalov,
Christoph Marquardt,
Johannes M. Fink, et al.
Linking classical microwave electrical circuits to the optical telecommunication band is at the core of modern communication. Future quantum information networks will require coherent microwave-to-optical conversion to link electronic quantum processors and memories via low-loss optical telecommunication networks. Efficient conversion can be achieved with electro-optical modulators operating at the single microwave photon level. In the standard electro-optic modulation scheme, this is impossible because both up-and down-converted sidebands are necessarily present. Here, we demonstrate true single-sideband up-or down-conversion in a triply resonant whispering gallery mode resonator by explicitly addressing modes with asymmetric free spectral range. Compared to previous experiments, we show a 3 orders of magnitude improvement of the electro-optical conversion efficiency, reaching 0.1% photon number conversion for a 10 GHz microwave tone at 0.42 mW of optical pump power. The presented scheme is fully compatible with existing superconducting 3D circuit quantum electrodynamics technology and can be used for nonclassical state conversion and communication. Our conversion bandwidth is larger than 1 MHz and is not fundamentally limited. (C) 2016 Optical Society of America
Evading Vacuum Noise: Wigner Projections or Husimi Samples?
C. R. Mueller,
C. Peuntinger,
T. Dirmeier,
I. Khan,
U. Vogl,
Ch. Marquardt,
G. Leuchs,
L. L. Sanchez-Soto,
Y. S. Teo, et al.
We investigate polarization squeezing in squeezed coherent states with varying coherent amplitudes. In contrast to the traditional characterization based on the full Stokes parameters, we experimentally determine the Stokes vector of each excitation subspace separately. Only for states with a fixed photon number do the methods coincide; when the photon number is indefinite, we parse the state in Fock layers, finding that substantially higher squeezing can be observed in some of the single layers. By capitalizing on the properties of the Husimi Q function, we map this notion onto the Poincare space, providing a full account of the measured squeezing.
Experimental generation of amplitude squeezed vector beams
Vanessa Chille,
Stefan Berg-Johansen,
Marion Semmler,
Peter Banzer,
Andrea Aiello,
Gerd Leuchs,
Christoph Marquardt
We present an experimental method for the generation of amplitude squeezed high-order vector beams. The light is modified twice by a spatial light modulator such that the vector beam is created by means of a collinear interferometric technique. A major advantage of this approach is that it avoids systematic losses, which are detrimental as they cause decoherence in continuous-variable quantum systems. The utilisation of a spatial light modulator (SLM) gives the flexibility to switch between arbitrary mode orders. The conversion efficiency with our setup is only limited by the efficiency of the SLM. We show the experimental generation of Laguerre-Gauss (LG) modes with radial indices 0 or 1 and azimuthal indices up to 3 with complex polarization structures and a quantum noise reduction up to -0.9dB +/- 0.1dB. The corresponding polarization structures are studied in detail by measuring the spatial distribution of the Stokes parameters. (C) 2016 Optical Society of America
Single-mode squeezing in arbitrary spatial modes
Marion Semmler,
Stefan Berg-Johansen,
Vanessa Chille,
Christian Gabriel,
Peter Banzer,
Andrea Aiello,
Christoph Marquardt,
Gerd Leuchs
As the generation of squeezed states of light has become a standard technique in laboratories, attention is increasingly directed towards adapting the optical parameters of squeezed beams to the specific requirements of individual applications. It is known that imaging, metrology, and quantum information may benefit from using squeezed light with a tailored transverse spatial mode. However, experiments have so far been limited to generating only a few squeezed spatial modes within a given setup. Here, we present the generation of single-mode squeezing in Laguerre-Gauss and Bessel-Gauss modes, as well as an arbitrary intensity pattern, all from a single setup using a spatial light modulator (SLM). The degree of squeezing obtained is limited mainly by the initial squeezing and diffractive losses introduced by the SLM, while no excess noise from the SLM is detectable at the measured sideband. The experiment illustrates the single-mode concept in quantum optics and demonstrates the viability of current SLMs as flexible tools for the spatial reshaping of squeezed light. (C) 2016 Optical Society of America
30 years of squeezed light generation
Ulrik L. Andersen,
Tobias Gehring,
Christoph Marquardt,
Gerd Leuchs
Squeezed light generation has come of age. Significant advances on squeezed light generation have been made over the last 30 years-from the initial, conceptual experiment in 1985 till today's top-tuned, application-oriented setups. Here we review the main experimental platforms for generating quadrature squeezed light that have been investigated in the last 30 years.
Nonlinear and quantum optics with whispering gallery resonators
Dmitry V. Strekalov,
Christoph Marquardt,
Andrey B. Matsko,
Harald G. L. Schwefel,
Gerd Leuchs
