958 research outputs found
Deterministic nano-assembly of a coupled quantum emitter - photonic crystal cavity system
The interaction of a single quantum emitter with its environment is a central
theme in quantum optics. When placed in highly confined optical fields, such as
those created in optical cavities or plasmonic structures, the optical
properties of the emitter can change drastically. In particular, photonic
crystal (PC) cavities show high quality factors combined with an extremely
small mode volume. Efficiently coupling a single quantum emitter to a PC cavity
is challenging because of the required positioning accuracy. Here, we
demonstrate deterministic coupling of single Nitrogen-Vacancy (NV) centers to
high-quality gallium phosphide PC cavities, by deterministically positioning
their 50 nm-sized host nanocrystals into the cavity mode maximum with
few-nanometer accuracy. The coupling results in a 25-fold enhancement of NV
center emission at the cavity wavelength. With this technique, the NV center
photoluminescence spectrum can be reshaped allowing for efficient generation of
coherent photons, providing new opportunities for quantum science.Comment: 13 pages, 4 figure
Nanopositioning of a diamond nanocrystal containing a single NV defect center
Precise control over the position of a single quantum object is important for
many experiments in quantum science and nanotechnology. We report on a
technique for high-accuracy positioning of individual diamond nanocrystals. The
positioning is done with a home-built nanomanipulator under real-time scanning
electron imaging, yielding an accuracy of a few nanometers. This technique is
applied to pick up, move and position a single NV defect center contained in a
diamond nanocrystal. We verify that the unique optical and spin properties of
the NV center are conserved by the positioning process.Comment: 3 pages, 3 figures; high-resolution version available at
http://www.ns.tudelft.nl/q
A Machine Learning Approach to Predicting Coverage in Random Wireless Networks
There is a rich literature on the prediction of coverage in random wireless networks using stochastic geometry. Though valuable, the existing stochastic geometry-based analytical expressions for coverage are only valid for a restricted set of oversimplified network scenarios. Deriving such expressions for more general and more realistic network scenarios has so far been proven intractable. In this work, we adopt a data-driven approach to derive a model that can predict the coverage probability in any random wireless network. We first show that the coverage probability can be accurately approximated by a parametrized sigmoid-like function. Then, by building large simulation-based datasets, the relationship between the wireless network parameters and the parameters of the sigmoid-like function is modeled using a neural network
Observation and control of hybrid spin-wave-Meissner-current transport modes
Superconductors are materials with zero electrical resistivity and the
ability to expel magnetic fields known as the Meissner effect. Their
dissipationless diamagnetic response is central to magnetic levitation and
circuits such as quantum interference devices. Here, we use superconducting
diamagnetism to shape the magnetic environment governing the transport of spin
waves - collective spin excitations in magnets that are promising on-chip
signal carriers - in a thin-film magnet. Using diamond-based magnetic imaging,
we observe hybridized spin-wave-Meissner-current transport modes with strongly
altered, temperature-tunable wavelengths. We extract the temperature-dependent
London penetration depth from the wavelength shifts and realize local control
of spin-wave refraction using a focused laser. Our results demonstrate the
versatility of superconductor-manipulated spin-wave transport and have
potential applications in spin-wave gratings, filters, crystals and cavities.Comment: main: 8 pages, 5 figures, supp: 15 pages, 6 figure
Receptor localization of steroid hormones and drugs: discoveries through the use of thaw-mount and dry-mount autoradiography
Decoherence-protected quantum gates for a hybrid solid-state spin register
Protecting the dynamics of coupled quantum systems from decoherence by the
environment is a key challenge for solid-state quantum information processing.
An idle qubit can be efficiently insulated from the outside world via dynamical
decoupling, as has recently been demonstrated for individual solid-state
qubits. However, protection of qubit coherence during a multi-qubit gate poses
a non-trivial problem: in general the decoupling disrupts the inter-qubit
dynamics, and hence conflicts with gate operation. This problem is particularly
salient for hybrid systems, wherein different types of qubits evolve and
decohere at vastly different rates. Here we present the integration of
dynamical decoupling into quantum gates for a paradigmatic hybrid system, the
electron-nuclear spin register. Our design harnesses the internal resonance in
the coupled-spin system to resolve the conflict between gate operation and
decoupling. We experimentally demonstrate these gates on a two-qubit register
in diamond operating at room temperature. Quantum tomography reveals that the
qubits involved in the gate operation are protected as accurately as idle
qubits. We further illustrate the power of our design by executing Grover's
quantum search algorithm, achieving fidelities above 90% even though the
execution time exceeds the electron spin dephasing time by two orders of
magnitude. Our results directly enable decoherence-protected interface gates
between different types of promising solid-state qubits. Ultimately, quantum
gates with integrated decoupling may enable reaching the accuracy threshold for
fault-tolerant quantum information processing with solid-state devices.Comment: This is original submitted version of the paper. The revised and
finalized version is in print, and is subjected to the embargo and other
editorial restrictions of the Nature journa
Cryptographic Primitives and Design Frameworks of Physical Layer Encryption for Wireless Communications
Security is always an important issue in wireless communications. Physical layer encryption (PLE) is an effective way to enhance wireless communication security and prevent eavesdropping. Rather than replacing cryptography at higher layers, PLE's benefit is to enable using lightweight cryptosystems or provide enhanced security at the signal level. The upper cryptography is faced with a noise-free channel, and the processing object is bit data. In PLE, the effects of channel and noise can be exploited to enhance security and prevent deciphering. In addition, since the processing object is complex vector signals, there are more operational functions to select and design for PLE. The mathematical models, design frameworks, and cryptographic primitives of PLE are established. Two design frameworks are proposed: stream PLE and block PLE. For stream PLE, a new 3D security constellation mapping is derived. For block PLE, two types of sub-transforms are defined: isometry transformations and stochastic transformations. Furthermore, a practical system operation mode PLE-block chaining (PBC) is proposed to enhance the practical system security. The proposed PLE framework can resist known plaintext attacks and chosen-plaintext attacks. The simulation shows that the proposed isometry transformation method has good performances in terms of bit error ratio (BER) penalty and confusion degree
Mathematical Model and Framework of Physical Layer Encryption for Wireless Communications
As a response to serious transmission security problems in wireless communications, physical layer encryption (PLE) provides an effective security measure which is very different from upper layer cryptography technologies. PLE can take advantage of the effects of channel and noise and the processing objects are complex vector signals, which are essentially different from Boolean algebra based traditional cryptography. This paper establishes mathematical models, design frameworks and cryptographic primitives for PLE. Two design frameworks are proposed: stream PLE and block PLE. For stream PLE, a new 3D security constellation mapping is derived. For block PLE, two types of sub-transforms are defined: isometry transformations and stochastic transformations. The proposed PLE framework has a large cipher signal space and key space; it provides more freedom in design and can resist known plaintext attacks and chosen-plaintext attacks
Intrusion detection systems for smart home IoT devices: experimental comparison study
Smart homes are one of the most promising applications of the emerging
Internet of Things (IoT) technology. With the growing number of IoT related
devices such as smart thermostats, smart fridges, smart speaker, smart light
bulbs and smart locks, smart homes promise to make our lives easier and more
comfortable. However, the increased deployment of such smart devices brings an
increase in potential security risks and home privacy breaches. In order to
overcome such risks, Intrusion Detection Systems are presented as pertinent
tools that can provide network-level protection for smart devices deployed in
home environments. These systems monitor the network activities of the smart
home-connected de-vices and focus on alerting suspicious or malicious activity.
They also can deal with detected abnormal activities by hindering the impostors
in accessing the victim devices. However, the employment of such systems in the
context of a smart home can be challenging due to the devices hardware
limitations, which may restrict their ability to counter the existing and
emerging attack vectors. Therefore, this paper proposes an experimental
comparison between the widely used open-source NIDSs namely Snort, Suricata and
Bro IDS to find the most appropriate one for smart homes in term of detection
accuracy and resources consumption including CP and memory utilization.
Experimental Results show that Suricata is the best performing NIDS for smart
homesComment: 7 pages, 4 figures, 2 table
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