Information Processing Devices Research Articles

Side-group chemical gating via reversible optical and electric control in a single molecule transistor

By taking advantage of large changes in geometric and electronic structure during the reversible trans–cis isomerisation, azobenzene derivatives have been widely studied for potential applications in information processing and digital storage devices. Here we report an unusual discovery of unambiguous conductance switching upon light and electric field-induced isomerisation of azobenzene in a robust single-molecule electronic device for the first time. Both experimental and theoretical data consistently demonstrate that the azobenzene sidegroup serves as a viable chemical gate controlled by electric field, which efficiently modulates the energy difference of trans and cis forms as well as the energy barrier of isomerisation. In conjunction with photoinduced switching at low biases, these results afford a chemically-gateable, fully-reversible, two-mode, single-molecule transistor, offering a fresh perspective for creating future multifunctional single-molecule optoelectronic devices in a practical way.

Coherent Excitation of Heterosymmetric Spin Waves with Ultrashort Wavelengths.

In the emerging field of magnonics, spin waves are foreseen as signal carriers for future spintronic information processing and communication devices, owing to both the very low power losses and a high device miniaturization potential predicted for short-wavelength spin waves. Yet, the efficient excitation and controlled propagation of nanoscale spin waves remains a severe challenge. Here, we report the observation of high-amplitude, ultrashort dipole-exchange spin waves (down to 80nm wavelength at 10GHz frequency) in a ferromagnetic single layer system, coherently excited by the driven dynamics of a spin vortex core. We used time-resolved x-ray microscopy to directly image such propagating spin waves and their excitation over a wide range of frequencies. By further analysis, we found that these waves exhibit a heterosymmetric mode profile, involving regions with anti-Larmor precession sense and purely linear magnetic oscillation. In particular, this mode profile consists of dynamic vortices with laterally alternating helicity, leading to a partial magnetic flux closure over the film thickness, which is explained by a strong and unexpected mode hybridization. This spin-wave phenomenon observed is a general effect inherent to the dynamics of sufficiently thick ferromagnetic single layer films, independent of the specific excitation method employed.

Ultra-low-loss integrated visible photonics using thin-film lithium niobate

Integrated photonics is a powerful platform that can improve the performance and stability of optical systems, while providing low-cost, small-footprint and scalable alternatives to implementations based on free-space optics. While great progress has been made on the development of low-loss integrated photonics platforms at telecom wavelengths, visible wavelength range has received less attention. Yet, many applications utilize visible or near-visible light, including those in optical imaging, optogenetics, and quantum science and technology. Here we demonstrate an ultra-low loss integrated visible photonics platform based on thin film lithium niobate on insulator. Our waveguides feature ultra-low propagation loss of 6 dB/m, while our microring resonators have an intrinsic quality factor of 11 million, both measured at 637 nm wavelength. Additionally, we demonstrate an on-chip visible intensity modulator with an electro-optic bandwidth of 10 GHz, limited by the detector used. The ultra-low loss devices demonstrated in this work, together with the strong second- and third-order nonlinearities in lithium niobate, open up new opportunities for creating novel passive, and active devices for frequency metrology and quantum information processing in the visible spectrum range.

Phase Stability of Spin-Crossover Nanoparticles Investigated by Synchrotron Mössbauer Spectroscopy and Small-Angle Neutron Scattering.

Spin-crossover nanomaterials have been actively studied in the past decade for their potential technological applications in sensing, actuating, and information processing devices. Unfortunately, an increasing number of the metallic centers become inactive at reduced sizes, presumably due to surface effects, limiting their switching ability and thus the scope of applications. Here we report on the investigation of "frozen" metallic centers in nanoparticles (2-80 nm size) of the spin-crossover compound Fe(pyrazine)[Ni(CN)4]. Magnetic measurements reveal both high-spin and low-spin residual fractions at atmospheric pressure. A pressure-induced transition of the high-spin residue is observed at around 1.5 GPa by synchrotron Mössbauer spectroscopy. We show that it is equivalent to a downshift of the transition temperature by ca. 400 K due to the size reduction. Unexpectedly, small-angle neutron scattering experiments demonstrate that these high-spin residual centers are not confined to the surface, which contradicts general theoretical considerations.

The discrete noise of magnons

We report experimental results, which show that the low-frequency noise of magnonic devices is dominated by the random telegraph signal noise rather than 1/f noise—a striking contrast to many electronic devices (f is a frequency). It was also found that the noise level of surface magnons depends strongly on the power level, increasing sharply at the on-set of nonlinear dissipation. The presence of the random telegraph signal noise suggests that the current fluctuations involve random discrete macro events caused by an individual macro-scale fluctuator. We anticipate that our results will help in developing the next generation of magnonic devices for information processing and sensing.

Dynamics Models of Synchronized Piecewise Linear Discrete Chaotic Systems of High Order

This paper deals with the methods for investigating the nonlinear dynamics of discrete chaotic systems (DCS) applied to piecewise linear systems of the third order. The paper proposes an approach to the analysis of the systems under research and their improvement. Thus, effective and mathematically sound methods for the analysis of nonlinear motions in the models under consideration are proposed. It makes it possible to obtain simple calculated relations for determining the basic dynamic characteristics of systems. Based on these methods, the authors developed algorithms for calculating the dynamic characteristics of discrete systems, i.e. areas of the existence of steady-state motion, areas of stability, capture band, and parameters of transients. By virtue of the developed methods and algorithms, the dynamic modes of several models of discrete phase synchronization systems can be analyzed. They are as follows: Pulsed and digital different orders, dual-ring systems of various types, including combined ones, and systems with cyclic interruption of auto-tuning. The efficiency of various devices for information processing, generation and stabilization could be increased by using the mentioned discrete synchronization systems on the grounds of the results of the analysis. We are now developing original software for analyzing the dynamic characteristics of various classes of discrete phase synchronization systems, based on the developed methods and algorithms.

On the freedom in representing quantum operations

We discuss the effects of a gauge freedom in representing quantum information processing devices, and its implications for characterizing these devices. We demonstrate with experimentally relevant examples that there exists equally valid descriptions of the same experiment which distribute errors differently among objects in a gate-set, leading to different error rates. Consequently, it can be misleading to attach a concrete operational meaning to figures of merit for individual gate-set elements. We propose an alternative operational figure of merit for a gate-set, the mean variation error, and a protocol for measuring this figure.

Distance-dependent memory for pictures and words

Abstract Three experiments explored the effect of medium of presentation (pictures, words) and psychological distance (proximal, distal) on episodic memory. In particular, we predicted that memory would be better for congruent combinations of medium and distance (i.e., pictures of psychologically proximal entities and verbal labels of psychologically distal entities) than incongruent combinations (i.e., pictures of psychologically distal entities and verbal labels of psychologically proximal entities). Our results support this hypothesis. In Experiments 1 and 2, recall was better when medium and temporal distance were congruent than not. In Experiment 3 people recognition was better when medium and spatial distance were congruent than not. These findings suggest that the decay of memory for details over time is a specific case of a broader principle that governs our memory system and is based on psychological distance between the individual and the target entity. More broadly, these results speak to the growing literature, which suggests that one of the major roles of memory is prospection. Within this framing, our findings suggest that the memory system serves prospection using qualitatively different information processing devices, depending on the psychological distance of the target from the individual.

Parity-Induced Thermalization Gap in Disordered Ring Lattices.

The gaps separating two different states widely exist in various physical systems: from the electrons in periodic lattices to the analogs in photonic, phononic, plasmonic systems, and even quasicrystals. Recently, a thermalization gap, an inaccessible range of photon statistics, was proposed for light in disordered structures [Nat. Phys. 11, 930 (2015)NPAHAX1745-247310.1038/nphys3482], which is intrinsically induced by the disorder-immune chiral symmetry and can be reflected by the photon statistics. The lattice topology was further identified as a decisive role in determining the photon statistics when the chiral symmetry is satisfied. Being very distinct from one-dimensional lattices, the photon statistics in ring lattices are dictated by its parity, i.e., odd or even sited. Here, we for the first time experimentally observe a parity-induced thermalization gap in strongly disordered ring photonic structures. In a limited scale, though the light tends to be localized, we are still able to find clear evidence of the parity-dependent disorder-immune chiral symmetry and the resulting thermalization gap by measuring photon statistics, while strong disorder-induced Anderson localization overwhelms such a phenomenon in larger-scale structures. Our results shed new light on the relation among symmetry, disorder, and localization, and may inspire new resources and artificial devices for information processing and quantum control on a photonic chip.

Dynamic holographic liquid crystal device containing nanoscale CuPc film

ABSTRACTIn this paper, CuPc-film-containing nematic liquid crystal (NLC) cells were fabricated, and dynamic holographic gratings recorded in the NLC cells were studied. The dependence of the diffraction efficiency on the applied voltage, light intensity, and the thicknesses of CuPc and NLC film was investigated. The high diffraction efficiency about 30% and the moderate build-up and erasing time in the order of magnitude of 0.1 s were achieved. The asymmetric energy transferring in two-beam coupling indicates photorefractive (PR) nature of the grating. The results of the photoinduced change of birefringence experiments suggest that the surface charge at the interface between the CuPc film and the NLC film plays a crucial role in the PR effect and the CuPc–NLC interface is mainly responsible for the formation of modulated surface charge layer and enables the photoelectric function of the NLC device. Our research may provide a new material option to optimise and develop NLC device for optical information processing and storage.

Tunable unconventional phonon blockade in Fabry-Perot cavity and optical parametric amplifier composite system

In this paper, we present a scheme to realize an unconventional photon blockade effect in a Fabry-Perot cavity and optical parametric amplifier (OPA) composite system. The system includes a tunable phase of complex driving strength, the second-order correlation function is used to describe the photon statistical properties. The numerical simulation of the photon blockade effect is conducted with different parameters. Our calculations show that the unconventional photon blockade effect can be controlled by the tunable phase of complex driving strength. Under the weak driving condition, the exact optimal conditions for strong photon anti-bunching are analytically derived (i.e. the optimal nonlinear gain of optical parametric amplifier and the phase of the field driving for the strong photon anti-bunching are obtained), and obtain the analytic calculations of the second-order correlation function. Under the optimal conditions, we perform a numerical simulation with different parameters. The optimal conditions for strong photon anti-bunching are found by analytic calculations, which are in good agreement with the numerical results. The results provide a platform for coherently operating the photon blockade and have potential applications in quantum information processing and quantum optical devices.

Uniform and directional growth of centimeter-sized single crystals of cyclodextrin-based metal organic frameworks

Although macroscopically-sized MOF crystals have proven of interest for efficient chromatographic separations, information processing, or optoelectronic devices, growing really large crystals has proven problematic. A growth-and-reseeding method can now produce MOF monocrystals ca. 1 cm3 in volume vs. at most ca. 0.025 cm3 by prior methods.

Nanomagnetic Particle-Based Information Processing

Understanding the physics of spintronic devices in the 3-nm size range can pave the way to next-generation energy-efficient information processing devices. To build a spin computer, a layer of 3-nm CoFe 2 O 4 nanoparticles was sandwiched as a central layer into the standard spin-transfer torque magnetic tunneling junction (STT-MTJ) stack. With further focused ion beam (FIB) trimming, a dual-layer junction consisting of one or more nanoparticles separating two CoFeB ferromagnetic layers was turned into a two-terminal spintronic device. The measured room-temperature electron transport through the device showed a staircase effect reminiscent of a single electron transport, which in addition depended on the relative orientations of the magnetic states of the ferromagnetic layers and the high-anisotropy ferrimagnetic nanoparticle. Besides having the staircase steps, the V-I curve indicated switching of the nanoparticles magnetization through the STT effect at currents of above 0.05 uA. The magnetoresistance (MR) curve of this device with the magnetic field applied perpendicular to the junction had an anomalous oscillatory field dependence in a relatively low field range of below 100 Oe.

Dilute Magnetic III-N Semiconductors Based on Rare Earth Doping

This paper focuses on the magnetic properties of wide bandgap III-N semiconductors doped with rare earth elements. Such materials form a novel class of dilute magnetic semiconductors that have an important potential impact on future information processing devices. In particular, rare earth doped III-N thin films may lead to integration of electronic, optical, and magnetic functionality for computation, sensing, and communication applications. The main aspects of this paper concern the efficient incorporation of rare earth ions in III-N thin films and the demonstration of magnetic effects at room temperature. While early studies were based on ion implantation and solid-state diffusion, major advances have been achieved through molecular beam epitaxy and metal-organic chemical vapor deposition. Measurements of room temperature magnetic effects from III-N films doped with rare earth elements, including erbium, gadolinium, europium, neodymium, and thulium, are presented. The dependence of measured magnetic properties on the synthesis method, co-doping, and material defects are addressed.

Quantum interference and correlation control of frequency-bin qubits

Quantum information is the next frontier in information science, promising unconditionally secure communications, enhanced channel capacities, and computing capabilities far beyond their classical counterparts. And as quantum information processing devices continue to transition from the lab to the field, the demand for the foundational infrastructure connecting them with each other and their users---the quantum internet---will only increase. Due to the remarkable success of frequency multiplexing and control in the classical internet, quantum information encoding in optical frequency offers an intriguing synergy with state-of-the-art fiber-optic networks. Yet coherent quantum frequency operations prove extremely challenging, due to the difficulties in mixing frequencies efficiently, arbitrarily, in parallel, and with low noise. Here we implement an original approach based on a reconfigurable quantum frequency processor, designed to perform arbitrary manipulations of spectrally encoded qubits. This processor's unique tunability allows us to demonstrate frequency-bin Hong-Ou-Mandel interference with record-high 94% visibility. Furthermore, by incorporating such tunability with our method's natural parallelizability, we synthesize independent quantum frequency gates in the same device, realizing the first high-fidelity flip of spectral correlations on two entangled photons. Compared to quantum frequency mixing approaches based on nonlinear optics, our linear method removes the need for additional pump fields and significantly reduces background noise. Our results demonstrate multiple functionalities in parallel in a single platform, representing a huge step forward for the frequency-multiplexed quantum internet.

Enhanced quantum coherence in exchange coupled spins via singlet-triplet transitions.

Manipulation of spin states at the single-atom scale underlies spin-based quantum information processing and spintronic devices. These applications require protection of the spin states against quantum decoherence due to interactions with the environment. While a single spin is easily disrupted, a coupled-spin system can resist decoherence by using a subspace of states that is immune to magnetic field fluctuations. Here, we engineered the magnetic interactions between the electron spins of two spin-1/2 atoms to create a "clock transition" and thus enhance their spin coherence. To construct and electrically access the desired spin structures, we use atom manipulation combined with electron spin resonance (ESR) in a scanning tunneling microscope. We show that a two-level system composed of a singlet state and a triplet state is insensitive to local and global magnetic field noise, resulting in much longer spin coherence times compared with individual atoms. Moreover, the spin decoherence resulting from the interaction with tunneling electrons is markedly reduced by a homodyne readout of ESR. These results demonstrate that atomically precise spin structures can be designed and assembled to yield enhanced quantum coherence.

Repeated multi-qubit readout and feedback with a mixed-species trapped-ion register.

Quantum error correction is essential for realizing the full potential of large-scale quantum information processing devices1,2. Fundamental to its experimental realization is the repetitive detection of errors via projective measurements of quantum correlations among qubits, as well as corrections using conditional feedback3. Repetitive application of such tasks requires that they neither induce unwanted crosstalk nor impede further control operations, which is challenging owing to the need to dissipatively couple qubits to the classical world for detection and reinitialization. For trapped ions, state readout involves scattering large numbers of resonant photons, which increases the probability of stray light causing errors on nearby qubits and leads to undesirable recoil heating of the ion motion. Here we demonstrate up to 50 sequential measurements of correlations between two beryllium ion microwave qubits using an ancillary optical qubit in a calcium ion, and implement feedback that allows us to stabilize two-qubit subspaces as well as Bell states, a class of maximally entangled states. Multi-qubit mixed-species gates are used to transfer information within the register from the qubit to the ancilla, enabling readout with negligible crosstalk to the data qubits. Heating of the ion motion during detection is mitigatedby recooling all three ions usinglight that interacts with onlythe calcium ion, known as sympathetic cooling. A key element of our experimental setup is a powerful classical control system that features flexible in-sequence processing for feedback control. The methods employed here provide essential tools for scaling trapped-ion quantum computing, quantum-state control and entanglement-enhanced quantum metrology4.

Beyond cognitive myopia: a patchwork approach to the concept of neural function

In this paper, I argue that looking at the concept of neural function through the lens of cognition alone risks cognitive myopia: it leads neuroscientists to focus only on mechanisms with cognitive functions that process behaviorally relevant information when conceptualizing “neural function”. Cognitive myopia tempts researchers to neglect neural mechanisms with noncognitive functions which do not process behaviorally relevant information but maintain and repair neural and other systems of the body. Cognitive myopia similarly affects philosophy of neuroscience because scholars overlook noncognitive functions when analyzing issues surrounding e.g., functional decomposition or the multifunctionality of neural structures. I argue that we can overcome cognitive myopia by adopting a patchwork approach that articulates cognitive and noncognitive “patches” of the concept of neural function. Cognitive patches describe mechanisms with causally specific effects on cognition and behavior which are likely operative in transforming sensory or other inputs into motor outputs. Noncognitive patches describe mechanisms that lack such specific effects; these mechanisms are enabling conditions for cognitive functions to occur. I use these distinctions to characterize two noncognitive functions at the mesoscale of neural circuits: subsistence functions like breathing are implemented by central pattern generators and are necessary to maintain the life of the organism. Infrastructural functions like gain control are implemented by canonical microcircuits and prevent neural system damage while cognitive processing occurs. By adding conceptual patches that describe these functions, a patchwork approach can overcome cognitive myopia and help us explain how the brain’s capacities as an information processing device are constrained by its ability to maintain and repair itself as a physiological apparatus.

Rhombohedral-Orthorhombic Ferroelectric Morphotropic Phase Boundary Associated with a Polar Vortex in BiFeO3 Films.

Strongly correlated oxides exhibit multiple degrees of freedoms, which can potentially mediate exotic phases with exciting physical properties, such as the polar vortex recently found in ferroelectric oxide films. A polar vortex is stabilized by competition between charge, lattice, and/or orbital degrees of freedom, which displays vortex-ferroelectric phase transitions and emergent chirality, making it a potential candidate for designing information storage and processing devices. Here, by a combination of controlled film growth and aberration-corrected scanning transmission electron microscopy, we obtain nanoscale vortex arrays in [110]-oriented BiFeO3 films. These vortex arrays are stabilized in ultrathin BiFeO3 layers sandwiched by two coherently grown orthorhombic scandate layers, exhibiting a ferroelectric morphotropic phase boundary constituted by a mixed-phase structure of polar orthorhombic BiFeO3 and rhombohedral BiFeO3. Clear polarization switching and piezoelectric signals were observed in these multilayers as revealed by piezoresponse force microscopy. This work presents a feature of a polar vortex in BiFeO3 films showing morphotropic phase boundary character, which offers a potential degree of manipulating phase components and properties of ferroelectric topological structures.

Polarization-selective spin wave driven domain-wall motion in antiferromagnets

The control of magnetic domain walls is essential for the magnetic-based memory and logic applications. As an elementary excitation of magnetic order, spin wave is capable of moving magnetic domain walls just as the conducting electric current. Ferromagnetic spin waves can only be right-circularly polarized. In contrast, antiferromagnetic spin waves have full polarization degree of freedom, including both left- and right-circular polarizations, as well as all possible linear or elliptical ones. Here we demonstrate that, due to the Dzyaloshinskii-Moriya interaction, the spin wave driven domain wall motion in antiferromagnets strongly depends on the linear polarization direction of the injected spin waves. Steering domain wall motion by simply tuning the polarization of spin waves offers new designing principles for domain-wall based information processing devices.