Towards Quantum Dynamics Simulation of Physical Systems: A Survey

After the emergence of quantum mechanics and realising its need for an accurate understanding of physical systems, numerical methods were being used to undergo quantum mechanical treatment. With increasing system correlations and size, numerical methods fell rather inefficient, and there was a need to simulate quantum mechanical phenomena on actual quantum computing hardware. Now, with noisy quantum computing machines that have been built and made available to use, realising quantum simulations are edging towards a practical reality. In this paper, we talk about the progress that has been made in the field of quantum simulations by actual quantum computing hardware and talk about some very fascinating fields where it has expanded its branches, too. Not only that, but we also review different software tool-sets available to date, which are to lay the foundation for realising quantum simulations in a much more comprehensive manner.Comment: 37 Pages with 13 Figures and 3 Table

Energy-preserving Indirect-feedback for Wireless Power Transfer

Recognising the limitations of various existing channel-estimation schemes for energy beamforming, we propose an energy-preserving indirect feedback-based approach for finding the optimal beamforming vector. Upon elaborating on the key ideas behind the proposed approach -- dynamics of the harvest-then-transmit protocol and the latency associated with the charging process -- we present an algorithm and its hardware architecture to concretise the proposed approach. The algorithm and the hardware architecture are supplemented by mathematical analysis, numerical simulation and hardware utilisation details, ASIC synthesis and post-layout simulation details, respectively. We firmly believe this paper, due to its unified algorithm-hardware design, will open up new avenues for research in radio frequency (RF) wireless power transfer.Comment: 29 pages, 12 figure

Electro-ionic control of surface plasmons in graphene-layered heterostructures

Precise control of light is indispensable to modern optical communication devices especially as the size of such devices approaches the subwavelength scale. Plasmonic devices are suitable for the development of these optical devices due to the extreme field confinement and its ability to be controlled by tuning the carrier density at the metal/dielectric interface. Here, an electro-ionic controlled plasmonic device consisting of Au/graphene/ion-gel is demonstrated as an optical switch, where an external electric field modulates the real part of the electrical conductivity. The graphene layer enhances charge penetration and charge separation at the Au/graphene interface resulting in an increased photoinduced voltage. The ion-gel immobilized on the Au/graphene further enables the electrical tunability of plasmons which modulates the intensity of the reflected laser light. This work paves the way for developing novel plasmonic electro-optic switches for potential applications such as integrated optical devices.Ministry of Education (MOE)National Research Foundation (NRF)J.Y.P. acknowledges NTU for the Research Student Scholarship and SC3DP which is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Medium-Sized Centre funding scheme. This work was supported in part by the Ministry of Education (MOE), Singapore - Academic Research Funding (AcRF) Tier 1 Grant RG192/17. R.M. and R.S.R. acknowledge Grants MOE2017- T2-2-129 and MOE2019-T2-1-058. M.B. acknowledges NTU for the NAP-SUG grant

Broad-energy oxygen ion implantation controlled magnetization dynamics in CoFeTaZr

In this paper, a novel pulsed broad energy spectrum ion-implantation technique, using the dense plasma focus device (DPF), for uniform oxygen-ion doping along the thickness of a ~250 nm thick magnetic CoFeTaZr layer is investigated. A new operational regime of the dense plasma focus – the off-focus mode – is explored to avoid the surface damage of the exposed sample by the high energy plasma streams/jets and instability accelerated ions, typically observed in conventional efficient-focus mode operation. The faraday cup measurements shows the increase in ion fluence from 3.83 × 1013 ion/cm2 for efficient-focus mode to 8.76 × 1013 ion/cm2 for off-focused mode operation in the broad-ion-energy range of 1–100 keV. The x-ray photoelectron spectroscopy (XPS) of the unexposed sample shows the presence of Co in Co0, Co2+ and Co3+, Fe in Fe0, Fe2+ and Fe3+, and Ta in Ta0 and Ta2+ oxidation states while Zr was observed with only metallic Zr binding energy peaks indicating the surface oxidation of the unexposed sample. The exposure to oxygen plasma in DPF device led to the increase in the higher oxidation states of Co, Fe and Ta with reduction in metallic binding energy peak and the deconvolution of oxygen XPS spectrum confirmed the bonding of oxygen to Co, Fe and Ta. The magnetization dynamics of unexposed and oxygen-ion doped samples was studied using magnetoimpedance measurements in the 1–2.5 GHz frequency range. Gilbert’s damping factor, in-plane anisotropy and effective magnetization of the magnetic substrate were calculated and it is found that these properties can be modulated with a lighter ion dosage using this novel pulsed broad-energy-ion implantation technique. It is concluded that the off-focus mode DPF operation can provide the ions of required energy and fluence to implant oxygen ions across the thickness of the CoFeTaZr magnetic thin film to modulate its magnetic properties.Ministry of Education (MOE)National Research Foundation (NRF)This research is supported by the Ministry of Education (MOE) under its Academic Research Fund Tier 1 (2018-T1-001-107), if applicable. R. Mahendiran acknowledges MOE, Singapore for support (Grant no.s R144-000-381-112 and R114-000-442-114). R. S. Rawat acknowledges MOE, Singapore for the support through MOE Tier 2 Grant, ARC-1/17 RSR (MOE2017-T2-2-129) and NRF, Singapore for the support through CRP Grant, CRP21-2018-0093

Piezoelectric strain control of terahertz spin current

Electrical control of photogenerated terahertz (THz) spin current pulses from a spintronic emitter has been at the forefront for the development of scalable, cost-efficient, wideband optospintronic devices. Artificially combined ferroelectric and ferromagnet heterostructure provides the potential avenue to deterministically control the phase of THz spin current pulse through piezoelectric strain. Here, the electric field-mediated piezoelectric strain control of photogenerated THz spin current pulse from a multiferroic spintronic emitter is demonstrated. The phase reversal of the THz spin current pulse is obtained from the combined effect of piezoelectric strain and a small magnetic field applied opposite to the initial magnetization of the ferromagnet. The piezoelectric strain-controlled phase switching of THz spin current thus opens a door to develop efficient strain engineered scalable on-chip THz spintronics devices.Ministry of Education (MOE)Nanyang Technological UniversityNational Research Foundation (NRF)Published versionA.C. acknowledges the NTU-Research Scholarship (NTU-RSS). R.M., S.G., and R.S.R. acknowledge the support from the Ministry of Education, Singapore (grant No. MOE2019-T2-1-058) (ARC 1/19 RSR) and National Research Foundation (grant No. NRF-CRP21-2018-0003). Z.L. and E.E.M.C. acknowledge the support from the Singapore Ministry of Education AcRF Tier 3 Programme “Geometrical Quantum Materials” (grant No. MOE2018-T3-1-002)′′and Singapore National Research Foundation Competitive Research Programme “The Next Generation of Spintronics with 2D Heterostructures” (grant No. NRF-CRP22-2019-0004). Y.F. also acknowledges the JSPS Grant-in-Aid (KAKENHI Nos. 18H01862a and 19K21112)