384 research outputs found
Toward quantum processing in molecules: A THz-bandwidth coherent memory for light
The unusual features of quantum mechanics are enabling the development of
technologies not possible with classical physics. These devices utilize
nonclassical phenomena in the states of atoms, ions, and solid-state media as
the basis for many prototypes. Here we investigate molecular states as a
distinct alternative. We demonstrate a memory for light based on storing
photons in the vibrations of hydrogen molecules. The THz-bandwidth molecular
memory is used to store 100-fs pulses for durations up to 1ns, enabling 10,000
operational time bins. The results demonstrate the promise of molecules for
constructing compact ultrafast quantum photonic technologies.Comment: 5 pages, 3 figures, 1 tabl
Ultrafast slow-light: Raman-induced delay of THz-bandwidth pulses
We propose and experimentally demonstrate a scheme to generate
optically-controlled delays based on off-resonant Raman absorption. Dispersion
in a transparency window between two neighboring, optically-activated Raman
absorption lines is used to reduce the group velocity of broadband 765 nm
pulses. We implement this approach in a potassium titanyl phosphate (KTP)
waveguide at room temperature, and demonstrate Raman-induced delays of up to
140 fs for a 650-fs duration, 1.8-THz bandwidth, signal pulse; the available
delay-bandwidth product is . Our approach is applicable to single
photon signals, offers wavelength tunability, and is a step toward processing
ultrafast photons.Comment: 5+4 pages, 4+2 figure
Extending electron orbital precession to the molecular case: Can orbital alignment be used to observe wavepacket dynamics?
The complexity of ultrafast molecular photoionization presents an obstacle to
the modelling of pump-probe experiments. Here, a simple optimized model of
atomic rubidium is combined with a molecular dynamics model to predict
quantitatively the results of a pump-probe experiment in which long range
rubidium dimers are first excited, then ionized after a variable delay. The
method is illustrated by the outline of two proposed feasible experiments and
the calculation of their outcomes. Both of these proposals use Feshbach 87Rb2
molecules. We show that long-range molecular pump-probe experiments should
observe spin-orbit precession given a suitable pump-pulse, and that the
associated high-frequency beat signal in the ionization probability decays
after a few tens of picoseconds. If the molecule was to be excited to only a
single fine structure state state, then a low-frequency oscillation in the
internuclear separation would be detectable through the timedependent
ionization cross section, giving a mechanism that would enable observation of
coherent vibrational motion in this molecule.Comment: 9 pages, 10 figures, PRA submissio
Time-bin to Polarization Conversion of Ultrafast Photonic Qubits
The encoding of quantum information in photonic time-bin qubits is apt for
long distance quantum communication schemes. In practice, due to technical
constraints such as detector response time, or the speed with which
co-polarized time-bins can be switched, other encodings, e.g. polarization, are
often preferred for operations like state detection. Here, we present the
conversion of qubits between polarization and time-bin encodings using a method
that is based on an ultrafast optical Kerr shutter and attain efficiencies of
97% and an average fidelity of 0.827+/-0.003 with shutter speeds near 1 ps. Our
demonstration delineates an essential requirement for the development of hybrid
and high-rate optical quantum networks
Characterisation of a single photon event camera for quantum imaging
We show a simple yet effective method that can be used to characterize the
per pixel quantum efficiency and temporal resolution of a single photon event
camera for quantum imaging applications. Utilizing photon pairs generated
through spontaneous parametric down-conversion, the detection efficiency of
each pixel, and the temporal resolution of the system, are extracted through
coincidence measurements. We use this method to evaluate the TPX3CAM, with
appended image intensifier, and measure an average efficiency of 7.4% and a
temporal resolution of 7.3ns. Furthermore, this technique reveals important
error mechanisms that can occur in post-processing. We expect that this
technique, and elements therein, will be useful to characterise other quantum
imaging systems.Comment: 9 pages, 5 figure
Reconfigurable phase contrast microscopy with correlated photon pairs
A phase-sensitive microscopy technique is proposed and demonstrated that
employs the momentum correlations inherent in spontaneous parametric
down-conversion. One photon from a correlated pair is focused onto a
microscopic target while the other is measured in the Fourier plane. This
provides knowledge of the position and angle of illumination for every photon
striking the target, allowing full post-production control of the illumination
angle used to form an image. The versatility of this approach is showcased with
asymmetric illumination and differential phase contrast imaging, without any
beam blocks or moving parts.Comment: 5 pages, 3 figure
Experimental investigation of high-dimensional quantum key distribution protocols with twisted photons
Quantum key distribution is on the verge of real world applications, where
perfectly secure information can be distributed among multiple parties. Several
quantum cryptographic protocols have been theoretically proposed and
independently realized in different experimental conditions. Here, we develop
an experimental platform based on high-dimensional orbital angular momentum
states of single photons that enables implementation of multiple quantum key
distribution protocols with a single experimental apparatus. Our versatile
approach allows us to experimentally survey different classes of quantum key
distribution techniques, such as the 1984 Bennett \& Brassard (BB84),
tomographic protocols including the six-state and the Singapore protocol, and
to investigate, for the first time, a recently introduced differential phase
shift (Chau15) protocol using twisted photons. This enables us to
experimentally compare the performance of these techniques and discuss their
benefits and deficiencies in terms of noise tolerance in different dimensions.Comment: 13 pages, 4 figures, 1 tabl
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