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Register a new userUsing Quantum Confinement to Uniquely Identify Devices
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Authors
J. Roberts
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Modern technology unintentionally provides resources that enable the trust of everyday interactions to be undermined. Some authentication schemes address this issue using devices that give unique outputs in response to a challenge. These signatures are generated by hard-to-predict physical responses derived from structural characteristics, which lend themselves to two different architectures, known as unique objects (UNOs) and physically unclonable functions (PUFs). The classical design of UNOs and PUFs limits their size and, in some cases, their security. Here we show that quantum confinement lends itself to the provision of unique identities at the nanoscale, by using fluctuations in tunnelling measurements through quantum wells in resonant tunnelling diodes (RTDs). This provides an uncomplicated measurement of identity without conventional resource limitations whilst providing robust security. The confined energy levels are highly sensitive to the specific nanostructure within each RTD, resulting in a distinct tunnelling spectrum for every device, as they contain a unique and unpredictable structure that is presently impossible to clone. This new class of authentication device operates with few resources in simple electronic structures above room temperature.
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Electrochemical ion insertion involves coupled ion-electron transfer reactions, transport of guest species, and redox of the host. The hosts are typically anisotropic solids with two-dimensional conduction planes, but can also be materials with one-dimensional or isotropic transport pathways. These insertion compounds have traditionally been studied in the context of energy storage, but also find extensive applications in electrocatalysis, optoelectronics, and computing. Recent developments in operando, ultrafast, and high-resolution characterization methods, as well as accurate theoretical simulation methods, have led to a renaissance in the understanding of ion-insertion compounds. In this Review, we present a unified framework for understanding insertion compounds across time and length scales ranging from atomic to device levels. Using graphite, transition metal dichalcogenides, layered oxides, oxyhydroxides, and olivines as examples, we explore commonalities in these materials in terms of point defects, interfacial reactions, and phase transformations. We illustrate similarities in the operating principles of various ion-insertion devices ranging from batteries and electrocatalysts to electrochromics and thermal transistors, with the goal of unifying research across disciplinary boundaries.
The boundary of topological superconductors might lead to the appearance of Majorana edge modes, whose non-trivial exchange statistics can be used for topological quantum computing. In branched nanowire networks one can exchange Majorana states by time-dependently tuning topologically non-trivial parameter regions. In this work, we simulate the exchange of four Majorana modes in T-shaped junctions made out of p-wave superconducting Rashba wires. We derive concrete experimental predictions for (quasi-)adiabatic braiding times and determine geometric conditions for successful Majorana exchange processes. Contrary to the widespread opinion, we show for the first time that in the adiabatic limit the gating time needs to be smaller than the inverse of the squared superconducting order parameter and scales linearly with the gating potential. Further, we show how to circumvent the formation of additional Majorana modes in branched nanowire systems, arising at wire intersection points of narrow junctions. Finally, we propose a multi qubit setup, which allows for universal and in particular topologically protected quantum computing.
Quantized magnetotransport is observed in 5.6 x 5.6 mm^2 epitaxial graphene devices, grown using highly constrained sublimation on the Si-face of SiC(0001) at high temperature (1900 {deg}C). The precise quantized Hall resistance of Rxy = h/2e^2 is maintained up to record level of critical current Ixx = 0.72 mA at T = 3.1 K and 9 T in a device where Raman microscopy reveals low and homogeneous strain. Adsorption-induced molecular doping in a second device reduced the carrier concentration close to the Dirac point(n ~ 1E10 (1/cm^2)), where mobility of 43700 cm^2/Vs is measured over an area of 10 mm^2. Atomic force, confocal optical, and Raman microscopies are used to characterize the large-scale devices, and reveal improved SiC terrace topography and the structure of the graphene layer. Our results show that the structural uniformity of epitaxial graphene produced by face-to-graphite processing contributes to millimeter-scale transport homogeneity, and will prove useful for scientific and commercial applications.
We propose a first-principles calculation to investigate the pressure-related transport properties of two kinds of pure monolayer black phosphorus (MBP) devices. Numerical results show that semi-conducting MBP can withstand a considerable compression pressure until it is transformed to be a conductor. The pure MBP devices can work as flexible electronic devices, negative pressure sensors, and positive pressure sensors depending on the chirality of BP and the magnitude of vertical pressure. When pressure is relatively small, the conductance is robust against the stress for zigzag MBP devices, while shows pressure-sensitive properties for armchair MBP devices. The pressure-stable property of zigzag MBP devices implies a good application prospects as flexible electronic devices, however, the distinct negative increase of conductance versus pressure indicates that armchair MBP devices can work as negative pressure sensors. When pressure is relatively large, both armchair MBP devices and zigzag MBP devices show favorable properties of positive pressure sensors, whose conductivities rise promptly versus pressure. The longer the device, the more the pressure sensitivity. Band alignment analysis and empirical Wentzel$-$Kramers$-$Brillouin (WKB) approximations are also performed to testify the tunneling process of pure MBP devices from first principles calculation.
Superradiance is the archetypical collective phenomenon where radiation is amplified by the coherence of emitters. It plays a prominent role in optics, where it enables the design of lasers with substantially reduced linewidths, quantum mechanics, and is even used to explain cosmological observations like Hawking radiation from black holes. Hybridization of distinct quantum systems allows to engineer new quantum metamaterials pooling the advantages of the individual systems. Superconducting circuits coupled to spin ensembles are promising future building blocks of integrated quantum devices and superradiance will play a prominent role. As such it is important to study its fundamental properties in hybrid devices. Experiments in the strong coupling regime have shown oscillatory behaviour in these systems but a clear signature of Dicke superradiance has been missing so far. Here we explore superradiance in a hybrid system composed of a superconducting resonator in the fast cavity limit inductively coupled to an inhomogeneously broadened ensemble of nitrogen-vacancy (NV) centres. We observe a superradiant pulse being emitted a trillion of times faster than the decay for an individual NV centre. This is further confirmed by the non-linear scaling of the emitted radiation intensity with respect to the ensemble size. Our work provides the foundation for future quantum technologies including solid state superradiant masers.
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