54 research outputs found
Real time demonstration of high bitrate quantum random number generation with coherent laser light
We present a random number generation scheme that uses broadband measurements
of the vacuum field contained in the radio-frequency sidebands of a single-mode
laser. Even though the measurements may contain technical noise, we show that
suitable algorithms can transform the digitized photocurrents into a string of
random numbers that can be made arbitrarily correlated with a subset of the
quantum fluctuations (high quantum correlation regime) or arbitrarily immune to
environmental fluctuations (high environmental immunity). We demonstrate up to
2 Gbps of real time random number generation that were verified using standard
randomness tests
Single-photon side bands
Single-photon states (and other non-Gaussian states) are typically studied in the time domain. In contrast, continuous-variable Gaussian states such as squeezed states are typically studied at side-band frequencies. Much of modern optical communication technology is also based on side-band techniques. Here we discuss what it means to produce single-photon states at side-band frequencies and propose techniques for producing and analyzing such states
Analysis of Imperfections in Practical Continuous-Variable Quantum Key Distribution
As quantum key distribution becomes a mature technology, it appears clearly
that some assumptions made in the security proofs cannot be justified in
practical implementations. This might open the door to possible side-channel
attacks. We examine several discrepancies between theoretical models and
experimental setups in the case of continuous-variable quantum key
distribution. We study in particular the impact of an imperfect modulation on
the security of Gaussian protocols and show that approximating the theoretical
Gaussian modulation with a discrete one is sufficient in practice. We also
address the issue of properly calibrating the detection setup, and in
particular the value of the shot noise. Finally, we consider the influence of
phase noise in the preparation stage of the protocol and argue that taking this
noise into account can improve the secret key rate because this source of noise
is not controlled by the eavesdropper.Comment: 4 figure
Gaussian Post-selection for Continuous Variable Quantum Cryptography
We extend the security proof for continuous variable quantum key distribution
protocols using post selection to account for arbitrary eavesdropping attacks
by employing the concept of an equivalent protocol where the post-selection is
implemented as a series of quantum operations including a virtual distillation.
We introduce a particular `Gaussian' post selection and demonstrate that the
security can be calculated using only experimentally accessible quantities.
Finally we explicitly evaluate the performance for the case of a noisy Gaussian
channel in the limit of unbounded key length and find improvements over all
pre-existing continuous variable protocols in realistic regimes.Comment: 4+4 pages. arXiv admin note: substantial text overlap with
arXiv:1106.082
Theoretical Analysis of an Ideal Noiseless Linear Amplifier for Einstein-Podolsky-Rosen Entanglement Distillation
We study the operational regime of a noiseless linear amplifier based on
quantum scissors that can nondeterministically amplify the one photon component
of a quantum state with weak excitation. It has been shown that an arbitrarily
large quantum state can be amplified by first splitting it into weak excitation
states using a network of beamsplitters. The output states of the network can
then be coherently recombined. In this paper, we analyse the performance of
such a device for distilling entanglement after transmission through a lossy
quantum channel, and look at two measures to determine the efficacy of the
noiseless linear amplifier. The measures used are the amount of entanglement
achievable and the final purity of the output amplified entangled state. We
study the performances of both a single and a two-element noiseless linear
amplifier for amplifying weakly excited states. Practically, we show that it
may be advantageous to work with a limited number of stages.Comment: 10 pages, 11 figure
Photon number discrimination without a photon counter and its application to reconstructing non-Gaussian states
The non-linearity of a conditional photon-counting measurement can be used to
`de-Gaussify' a Gaussian state of light. Here we present and experimentally
demonstrate a technique for photon number resolution using only homodyne
detection. We then apply this technique to inform a conditional measurement;
unambiguously reconstructing the statistics of the non-Gaussian one and two
photon subtracted squeezed vacuum states. Although our photon number
measurement relies on ensemble averages and cannot be used to prepare
non-Gaussian states of light, its high efficiency, photon number resolving
capabilities, and compatibility with the telecommunications band make it
suitable for quantum information tasks relying on the outcomes of mean values.Comment: 4 pages, 3 figures. Theory section expanded in response to referee
comment
A Scalable, Self-Analyzing Digital Locking System for use on Quantum Optics Experiments
Digital control of optics experiments has many advantages over analog control
systems, specifically in terms of scalability, cost, flexibility, and the
integration of system information into one location. We present a digital
control system, freely available for download online, specifically designed for
quantum optics experiments that allows for automatic and sequential re-locking
of optical components. We show how the inbuilt locking analysis tools,
including a white-noise network analyzer, can be used to help optimize
individual locks, and verify the long term stability of the digital system.
Finally, we present an example of the benefits of digital locking for quantum
optics by applying the code to a specific experiment used to characterize
optical Schrodinger cat states.Comment: 7 pages, 5 figure
Quantum State Engineering with Continuous-Variable Post-Selection
We present a scheme to conditionally engineer an optical quantum system via
continuous-variable measurements. This scheme yields high-fidelity squeezed
single photon and superposition of coherent states, from input single and two
photon Fock states respectively. The input Fock state is interacted with an
ancilla squeezed vacuum state using a beam-splitter. We transform the quantum
system by post-selecting on the continuous-observable measurement outcome of
the ancilla state. We experimentally demonstrate the principles of this scheme
using displaced coherent states and measure experimentally fidelities that are
only achievable using quantum resources.Comment: 4 pages, 5 figures, publishe
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