15 research outputs found
Continuous phase stabilization and active interferometer control using two modes
We present a computer-based active interferometer stabilization method that
can be set to an arbitrary phase difference and does not rely on modulation of
the interfering beams. The scheme utilizes two orthogonal modes propagating
through the interferometer with a constant phase difference between them to
extract a common phase and generate a linear feedback signal. Switching times
of 50ms over a range of 0 to 6 pi radians at 632.8nm are experimentally
demonstrated. The phase can be stabilized up to several days to within 3
degrees.Comment: 3 pages, 2 figure
Photon Number Statistics of Multimode Parametric Down-Conversion
We experimentally analyze the complete photon number statistics of parametric
downconversion and ascertain the influence of multimode effects. Our results
clearly reveal a difference between single mode theoretical description and the
measured distributions. Further investigations assure the applicability of
loss-tolerant photon number reconstruction and prove strict photon number
correlation between signal and idler modes.Comment: 5 pages, 3 figure
Absolute efficiency estimation of photon-number-resolving detectors using twin beams
A nonclassical light source is used to demonstrate experimentally the
absolute efficiency calibration of a photon-number-resolving detector. The
photon-pair detector calibration method developed by Klyshko for single-photon
detectors is generalized to take advantage of the higher dynamic range and
additional information provided by photon-number-resolving detectors. This
enables the use of brighter twin-beam sources including amplified pulse pumped
sources, which increases the relevant signal and provides measurement
redundancy, making the calibration more robust
Measuring Measurement: Theory and Practice
Recent efforts have applied quantum tomography techniques to the calibration
and characterization of complex quantum detectors using minimal assumptions. In
this work we provide detail and insight concerning the formalism, the
experimental and theoretical challenges and the scope of these tomographical
tools. Our focus is on the detection of photons with avalanche photodiodes and
photon number resolving detectors and our approach is to fully characterize the
quantum operators describing these detectors with a minimal set of well
specified assumptions. The formalism is completely general and can be applied
to a wide range of detectorsComment: 22 pages, 27 figure
Mapping coherence in measurement via full quantum tomography of a hybrid optical detector
Quantum states and measurements exhibit wave-like --- continuous, or
particle-like --- discrete, character. Hybrid discrete-continuous photonic
systems are key to investigating fundamental quantum phenomena, generating
superpositions of macroscopic states, and form essential resources for
quantum-enhanced applications, e.g. entanglement distillation and quantum
computation, as well as highly efficient optical telecommunications. Realizing
the full potential of these hybrid systems requires quantum-optical
measurements sensitive to complementary observables such as field quadrature
amplitude and photon number. However, a thorough understanding of the practical
performance of an optical detector interpolating between these two regions is
absent. Here, we report the implementation of full quantum detector tomography,
enabling the characterization of the simultaneous wave and photon-number
sensitivities of quantum-optical detectors. This yields the largest
parametrization to-date in quantum tomography experiments, requiring the
development of novel theoretical tools. Our results reveal the role of
coherence in quantum measurements and demonstrate the tunability of hybrid
quantum-optical detectors.Comment: 7 pages, 3 figure
Avalanche Photo-Detection for High Data Rate Applications
Avalanche photo detection is commonly used in applications which require
single photon sensitivity. We examine the limits of using avalanche photo
diodes (APD) for characterising photon statistics at high data rates. To
identify the regime of linear APD operation we employ a ps-pulsed diode laser
with variable repetition rates between 0.5MHz and 80MHz. We modify the mean
optical power of the coherent pulses by applying different levels of
well-calibrated attenuation. The linearity at high repetition rates is limited
by the APD dead time and a non-linear response arises at higher photon-numbers
due to multiphoton events. Assuming Poissonian input light statistics we
ascertain the effective mean photon-number of the incident light with high
accuracy. Time multiplexed detectors (TMD) allow to accomplish photon- number
resolution by photon chopping. This detection setup extends the linear response
function to higher photon-numbers and statistical methods may be used to
compensate for non-linearity. We investigated this effect, compare it to the
single APD case and show the validity of the convolution treatment in the TMD
data analysis.Comment: 16 pages, 5 figure
Manipulating the quantum information of the radial modes of trapped ions: Linear phononics, entanglement generation, quantum state transmission and non-locality tests
We present a detailed study on the possibility of manipulating quantum
information encoded in the "radial" modes of arrays of trapped ions (i.e., in
the ions' oscillations orthogonal to the trap's main axis). In such systems,
because of the tightness of transverse confinement, the radial modes pertaining
to different ions can be addressed individually. In the first part of the paper
we show that, if local control of the radial trapping frequencies is available,
any linear optical and squeezing operation on the locally defined modes - on
single as well as on many modes - can be reproduced by manipulating the
frequencies. Then, we proceed to describe schemes apt to generate unprecedented
degrees of bipartite and multipartite continuous variable entanglement under
realistic noisy working conditions, and even restricting only to a global
control of the trapping frequencies. Furthermore, we consider the transmission
of the quantum information encoded in the radial modes along the array of ions,
and show it to be possible to a remarkable degree of accuracy, for both
finite-dimensional and continuous variable quantum states. Finally, as an
application, we show that the states which can be generated in this setting
allow for the violation of multipartite non-locality tests, by feasible
displaced parity measurements. Such a demonstration would be a first test of
quantum non-locality for "massive" degrees of freedom (i.e., for degrees of
freedom describing the motion of massive particles).Comment: 21 pages; this paper, presenting a far more extensive and detailed
analysis, completely supersedes arXiv:0708.085
Integrated Photonic Sensing
Loss is a critical roadblock to achieving photonic quantum-enhanced
technologies. We explore a modular platform for implementing integrated
photonics experiments and consider the effects of loss at different stages of
these experiments, including state preparation, manipulation and measurement.
We frame our discussion mainly in the context of quantum sensing and focus
particularly on the use of loss-tolerant Holland-Burnett states for optical
phase estimation. In particular, we discuss spontaneous four-wave mixing in
standard birefringent fibre as a source of pure, heralded single photons and
present methods of optimising such sources. We also outline a route to
programmable circuits which allow the control of photonic interactions even in
the presence of fabrication imperfections and describe a ratiometric
characterisation method for beam splitters which allows the characterisation of
complex circuits without the need for full process tomography. Finally, we
present a framework for performing state tomography on heralded states using
lossy measurement devices. This is motivated by a calculation of the effects of
fabrication imperfections on precision measurement using Holland-Burnett
states.Comment: 19 pages, 7 figure
Detector decoy quantum key distribution
Photon number resolving detectors can enhance the performance of many
practical quantum cryptographic setups. In this paper, we employ a simple
method to estimate the statistics provided by such a photon number resolving
detector using only a threshold detector together with a variable attenuator.
This idea is similar in spirit to that of the decoy state technique, and is
specially suited for those scenarios where only a few parameters of the photon
number statistics of the incoming signals have to be estimated. As an
illustration of the potential applicability of the method in quantum
communication protocols, we use it to prove security of an entanglement based
quantum key distribution scheme with an untrusted source without the need of a
squash model and by solely using this extra idea. In this sense, this detector
decoy method can be seen as a different conceptual approach to adapt a single
photon security proof to its physical, full optical implementation. We show
that in this scenario the legitimate users can now even discard the double
click events from the raw key data without compromising the security of the
scheme, and we present simulations on the performance of the BB84 and the
6-state quantum key distribution protocols.Comment: 27 pages, 7 figure
Measuring measurement
Measurement connects the world of quantum phenomena to the world of classical
events. It plays both a passive role, observing quantum systems, and an active
one, preparing quantum states and controlling them. Surprisingly - in the light
of the central status of measurement in quantum mechanics - there is no general
recipe for designing a detector that measures a given observable. Compounding
this, the characterization of existing detectors is typically based on partial
calibrations or elaborate models. Thus, experimental specification (i.e.
tomography) of a detector is of fundamental and practical importance. Here, we
present the realization of quantum detector tomography: we identify the optimal
positive-operator-valued measure describing the detector, with no ancillary
assumptions. This result completes the triad, state, process, and detector
tomography, required to fully specify an experiment. We characterize an
avalanche photodiode and a photon number resolving detector capable of
detecting up to eight photons. This creates a new set of tools for accurately
detecting and preparing non-classical light.Comment: 6 pages, 4 figures,see video abstract at
http://www.quantiki.org/video_abstracts/0807244