2,028 research outputs found
Silicon-Nitride Platform for Narrowband Entangled Photon Generation
CMOS-compatible photonic chips are highly desirable for real-world quantum
optics devices due to their scalability, robustness, and integration with
electronics. Despite impressive advances using Silicon nanostructures,
challenges remain in reducing their linear and nonlinear losses and in creating
narrowband photons necessary for interfacing with quantum memories. Here we
demonstrate the potential of the silicon nitride (Si3N4) platform by realizing
an ultracompact, bright, entangled photon-pair source with selectable photon
bandwidths down to 30 MHz, which is unprecedented for an integrated source.
Leveraging Si3N4's moderate thermal expansion, simple temperature control of
the chip enables precise wavelength stabilization and tunability without active
control. Single-mode photon pairs at 1550 nm are generated at rates exceeding
107 s-1 with mW's of pump power and are used to produce time-bin entanglement.
Moreover, Si3N4 allows for operation from the visible to the mid-IR, which make
it highly promising for a wide range of integrated quantum photonics
applications.Comment: Please don't hesitate to email comments and suggestion
Efficient quantum state transfer in spin chains via adiabatic passage
We propose a method for quantum state transfer in spin chains using an
adiabatic passage technique. Modifying even and odd nearest-neighbour couplings
in time allows to achieve transfer fidelities arbitrarily close to one, without
the need for a precise control of coupling strengths and timing. We study in
detail transfer by adiabatic passage in a spin-1 chain governed by a
generalized Heisenberg Hamiltonian. We consider optimization of the transfer
process applying optimal control techniques. We discuss a realistic
experimental implementation using cold atomic gases confined in deep optical
lattices.Comment: 14 pages, 6 figures, to be published in New J. Phy
Architectures for a quantum random access memory
A random access memory, or RAM, is a device that, when interrogated, returns
the content of a memory location in a memory array. A quantum RAM, or qRAM,
allows one to access superpositions of memory sites, which may contain either
quantum or classical information. RAMs and qRAMs with n-bit addresses can
access 2^n memory sites. Any design for a RAM or qRAM then requires O(2^n)
two-bit logic gates. At first sight this requirement might seem to make large
scale quantum versions of such devices impractical, due to the difficulty of
constructing and operating coherent devices with large numbers of quantum logic
gates. Here we analyze two different RAM architectures (the conventional fanout
and the "bucket brigade") and propose some proof-of-principle implementations
which show that in principle only O(n) two-qubit physical interactions need
take place during each qRAM call. That is, although a qRAM needs O(2^n) quantum
logic gates, only O(n) need to be activated during a memory call. The resulting
decrease in resources could give rise to the construction of large qRAMs that
could operate without the need for extensive quantum error correction.Comment: 10 pages, 7 figures. Updated version includes the answers to the
Refere
Digital-Analog Quantum Simulations with Superconducting Circuits
Quantum simulations consist in the intentional reproduction of physical or
unphysical models into another more controllable quantum system. Beyond
establishing communication vessels between unconnected fields, they promise to
solve complex problems which may be considered as intractable for classical
computers. From a historic perspective, two independent approaches have been
pursued, namely, digital and analog quantum simulations. The former usually
provide universality and flexibility, while the latter allows for better
scalability. Here, we review recent literature merging both paradigms in the
context of superconducting circuits, yielding: digital-analog quantum
simulations. In this manner, we aim at getting the best of both approaches in
the most advanced quantum platform involving superconducting qubits and
microwave transmission lines. The discussed merge of quantum simulation
concepts, digital and analog, may open the possibility in the near future for
outperforming classical computers in relevant problems, enabling the reach of a
quantum advantage.Comment: Review article, 26 pages, 4 figure
Advanced optical modulation and fast reconfigurable en/decoding techniques for OCDMA application
With the explosive growth of bandwidth requirement in optical fiber communication
networks, optical code division multiple access (OCDMA) has witnessed tremendous
achievements as one of the promising technologies for optical access networks over the
past decades. In an OCDMA system, optical code processing is one of the key
techniques. Rapid optical code reconfiguration can improve flexibility and security of
the OCDMA system. This thesis focuses on advanced optical modulations and
en/decoding techniques for applications in fast reconfigurable OCDMA systems and
secure optical communications.
A novel time domain spectral phase encoding (SPE) scheme which can rapidly
reconfigure the optical code and is compatible with conventional spectral domain phase
en/decoding by using a pair of dispersive devices and a high speed phase modulator is
proposed. Based on this scheme, a novel advanced modulation technique that can
simultaneously generate both the optical code and the differential-phase-shift-keying
(DPSK) data using a single phase modulator is experimentally demonstrated. A
symmetric time domain spectral phase encoding and decoding (SPE/SPD) scheme using
a similar setup for both the transmitter and receiver is further proposed, based on which
a bit-by-bit optical code scrambling and DPSK data modulation technique for secure
optical communications has been successfully demonstrated. By combining optical
encoding and optical steganography, a novel approach for secure transmission of time
domain spectral phase encoded on-off-keying (OOK)/DPSK-OCDMA signal over
public wavelength-division multiplexing (WDM) network has also been proposed and
demonstrated.
To enable high speed operation of the time domain SPE/SPD scheme and enhance the
system security, a rapid programmable, code-length variable bit-by-bit optical code
shifting technique is proposed. Based on this technique, security improvements for
OOK/DPSK OCDMA systems at data rates of 10Gb/s and 40Gb/s using reconfigurable
optical codes of up to 1024-chip have been achieved.
Finally, a novel tunable two-dimensional coherent optical en/decoder which can
simultaneously perform wavelength hopping and spectral phase encoding based on
coupled micro-ring resonator is proposed and theoretically investigated. The techniques
included in this thesis could be potentially used for future fast reconfigurable and secure
optical code based communication systems
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