385 research outputs found
Controlling phonons and photons at the wavelength-scale: silicon photonics meets silicon phononics
Radio-frequency communication systems have long used bulk- and
surface-acoustic-wave devices supporting ultrasonic mechanical waves to
manipulate and sense signals. These devices have greatly improved our ability
to process microwaves by interfacing them to orders-of-magnitude slower and
lower loss mechanical fields. In parallel, long-distance communications have
been dominated by low-loss infrared optical photons. As electrical signal
processing and transmission approaches physical limits imposed by energy
dissipation, optical links are now being actively considered for mobile and
cloud technologies. Thus there is a strong driver for wavelength-scale
mechanical wave or "phononic" circuitry fabricated by scalable semiconductor
processes. With the advent of these circuits, new micro- and nanostructures
that combine electrical, optical and mechanical elements have emerged. In these
devices, such as optomechanical waveguides and resonators, optical photons and
gigahertz phonons are ideally matched to one another as both have wavelengths
on the order of micrometers. The development of phononic circuits has thus
emerged as a vibrant field of research pursued for optical signal processing
and sensing applications as well as emerging quantum technologies. In this
review, we discuss the key physics and figures of merit underpinning this
field. We also summarize the state of the art in nanoscale electro- and
optomechanical systems with a focus on scalable platforms such as silicon.
Finally, we give perspectives on what these new systems may bring and what
challenges they face in the coming years. In particular, we believe hybrid
electro- and optomechanical devices incorporating highly coherent and compact
mechanical elements on a chip have significant untapped potential for
electro-optic modulation, quantum microwave-to-optical photon conversion,
sensing and microwave signal processing.Comment: 26 pages, 5 figure
Data security in photonic information systems using quantum based approaches
The last two decades has seen a revolution in how information is stored and transmitted
across the world. In this digital age, it is vital for banking systems, governments and
businesses that this information can be transmitted to authorised receivers quickly and
efficiently. Current classical cryptosystems rely on the computational difficulty of
calculating certain mathematical functions but with the advent of quantum computers,
implementing efficient quantum algorithms, these systems could be rendered insecure
overnight. Quantum mechanics thankfully also provides the solution, in which
information is transmitted on single-photons called qubits and any attempt by an
adversary to gain information on these qubits is limited by the laws of quantum
mechanics.
This thesis looks at three distinct different quantum information experiments. Two of
the systems describe the implementation of distributing quantum keys, in which the
presence of an eavesdropper introduces unavoidable errors by the laws of quantum
mechanics. The first scheme used a quantum dot in a micropillar cavity as a singlephoton
source. A polarisation encoding scheme was used for implementing the BB84,
quantum cryptographic protocol, which operated at a wavelength of 905 nm and a clock
frequency of 40 MHz. A second system implemented phase encoding using asymmetric
unbalanced Mach-Zehnder interferometers, with a weak coherent source, operating at a
wavelength of 850 nm and pulsed at a clock rate of 1 GHz. The system used
depolarised light propagating in the fibre quantum channel. This helps to eliminate the
random evolution of the state of polarisation of photons, as a result of stress induced
changes in the intrinsic birefringence of the fibre. The system operated completely
autonomously, using custom software to compensate for path length fluctuations in the
arms of the interferometer and used a variety of different single-photon detector
technologies. The final quantum information scheme looked at quantum digital
signatures, which allows a sender, Alice, to distribute quantum signatures to two parties,
Bob and Charlie, such that they are able to authenticate that the message originated
from Alice and that the message was not altered in transmission
Superconducting nanowire single-photon detectors: physics and applications
Single-photon detectors based on superconducting nanowires (SSPDs or SNSPDs)
have rapidly emerged as a highly promising photon-counting technology for
infrared wavelengths. These devices offer high efficiency, low dark counts and
excellent timing resolution. In this review, we consider the basic SNSPD
operating principle and models of device behaviour. We give an overview of the
evolution of SNSPD device design and the improvements in performance which have
been achieved. We also evaluate device limitations and noise mechanisms. We
survey practical refrigeration technologies and optical coupling schemes for
SNSPDs. Finally we summarize promising application areas, ranging from quantum
cryptography to remote sensing. Our goal is to capture a detailed snapshot of
an emerging superconducting detector technology on the threshold of maturity.Comment: 27 pages, 5 figures, Review article preprint versio
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