• Issue

    Advanced Quantum Technologies: Volume 4, Issue 1

    January 2021

Cover Picture

Free Access

Front Cover: Enhanced Spin Hall Effect in S-Implanted Pt (Adv. Quantum Technol. 1/2021)

  • First Published: 15 January 2021
Description unavailable

The spin Hall effect is a spin–orbit-coupling-related phenomenon, in which the charge current generates a transverse spin current and vice versa. Platinum is a well explored spin Hall material due to large spin–orbit coupling and high conductivity, but its interconversion efficiency is of around 10% only. In article number 2000112, Surbhi Gupta, Yasuhiro Fukuma, and co-workers employ the pioneering technology of ion implantation to develop a new spin Hall material, sulfur-implanted platinum Pt(S), demonstrating an interconversion efficiency of 50%. The designed Pt(S) achieves high spin Hall conductivity, which determines its suitability for next-generation spin–orbit-torque-driven logic and memory device applications.

Back Cover

Free Access

Back Cover: The Origin of Quantum Effects in Low-Dimensional Thermoelectric Materials (Adv. Quantum Technol. 1/2021)

  • First Published: 15 January 2021
Description unavailable

In article number 2000115, Nguyen Tuan Hung and Riichiro Saito report on the origin of the quantum effects to improve the thermoelectricity of low-dimensional materials. The power factor enhances when the confinement length (diameter of 1D materials or the thickness of 2D materials) is smaller than the thermal de Broglie wavelength, which is established as a crucial parameter to enhance the thermoelectricity. The cover image depicts electrons moving from hot to cold temperature, which can generate electrical energy. The quantum effect occurs when the width of the system is smaller than the thermal de Broglie wavelength.

Masthead

Free Access

Masthead (Adv. Quantum Technol. 1/2021)

  • First Published: 15 January 2021

Reviews

Recent Advances on Quantum Key Distribution Overcoming the Linear Secret Key Capacity Bound

  • First Published: 25 November 2020
Description unavailable

This article presents an up-to-date survey on recent developments on quantum key distribution (QKD) overcoming the linear secret key capacity bound, including the security proofs of twin-field (TF) QKD, phase-matching QKD, and other TF-QKD type protocols, the theoretical examinations of these protocols under realistic conditions, and the recent experimental demonstrations.

The Origin of Quantum Effects in Low-Dimensional Thermoelectric Materials

  • First Published: 03 December 2020
Description unavailable

Hicks and Dresselhaus in 1993 have theoretically predicted that thermoelectricity is enhanced by the confinement of electrons in low-dimensional materials. However, experimentalists cannot answer the question, what kind of materials would give effective performance by the confinement effect. In this report, the authors discuss the reason why the thermal de Broglie wavelength becomes a crucial parameter to enhance thermoelectricity.

Communications

Observation of Shubnikov–de Haas Oscillations, Planar Hall Effect, and Anisotropic Magnetoresistance at the Conducting Interface of EuO–KTaO3

  • First Published: 14 December 2020
Description unavailable

2D electron gas (2DEG) at oxide interfaces with Rashba spin-split bands is promising for spin-electronic devices. Analyzing Shubnikov–de Haas oscillations, the authors report the presence of Rashba spin-split bands for the 2DEG present at the interface of EuO–KTaO3. From the transport data, the authors draw a possible band diagram and conclude that the conical point of the energy spectrum is topological.

Enhanced Spin Hall Effect in S-Implanted Pt

  • First Published: 03 December 2020
Description unavailable

The present work proposes a new spin Hall material, Pt(S), designed by 12 keV sulfur (S)-ion implantation in platinum (Pt), which demonstrates eight times (three times) enhanced charge-to-spin interconversion efficiency at 10 K (300 K). Furthermore, its large spin Hall conductivity of ≈8.32 × 105 ( 2 e ) Ω–1 m–1 among the reported pure Pt and other derivative alloys dictates the suitability of Pt(S) for next-generation spin–orbit-torque-driven logic and memory device applications.

Full Papers

Variational Quantum Generators: Generative Adversarial Quantum Machine Learning for Continuous Distributions

  • First Published: 03 December 2020
Description unavailable

Continuous classical probability distributions are modeled using hybrid quantum–classical generative adversarial networks, where both generator and discriminator consist of a quantum encoder, that maps classical information to quantum states, and a variational circuit. Classical distributions are obtained by sampling the generator and measuring observables on the states generated. This framework provides a blueprint for designing hybrid quantum–classical machine learning architectures.

Open Access

Control of the Half-Skyrmion Hall Effect and Its Application to Adder–Subtractor

  • First Published: 19 November 2020
Description unavailable

Precise control of a half-skyrmion motion by deforming the internal structure of skyrmions is experimentally and theoretically demonstrated by utilizing external magnetic field. Furthermore, the distinct advantages of half-skyrmions help to realize the potential of half-skyrmions application beyond skyrmion-based electronics by introducing addition/subtraction operation.

Multiferroic BaCoX2O7 (X = P, As) Compounds with Incommensurate Structural Waves but Collinear Spin Ingredients

  • First Published: 09 November 2020
Description unavailable

BaCo(P,As)2O7 is shown to be a type-II multiferroics based on an original scenario in which incommensurate atomic shifts and collinear antiferromagnetic (AFM) Ising spins interact as crucial ingredients. In comparison no magnetoelectric coupling is detected in the Heisenberg BaFeP2O7 isomorph, with strong spin-lattice coupling leading to a modulated AFM spin structure. Magnetic dipole–dipole interactions are discriminating between them.

Open Access

Different Types of Photon Entanglement from a Constantly Driven Quantum Emitter Inside a Cavity

  • First Published: 14 December 2020
Description unavailable

Entangled photon states are at the heart of quantum physics, most prominent being the maximally entangled Bell states. Analyzing a driven four-level emitter–cavity system, it is demonstrated that two different types of entanglement and special points with vanishing concurrence emerge, depending on the resonance and excitation conditions. All results are well explained using analytic expressions.