Transport Properties of a Quantum Dot and a Quantum Ring in Series

서민기,정윤철 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.1

The decoherence mechanism of an electron interferometer is studied by using a serial quantum dot and ring device. By coupling a quantum dot to a quantum ring (closed-loop electron interferometer), we were able to observe both Coulomb oscillations and Aharonov-Bohm interference simultaneously. The coupled device behaves like an ordinary double quantum dot at zero magnetic field while the conductance of the Coulomb blockade peak is modulated by the electron interference at finite magnetic fields. By injecting one electron at a time (by exploiting the sequential tunneling of a quantum dot) into the interferometer, we were able to study the visibility of the electron interference at non-zero bias voltage. The visibility was found to decay rapidly as the electron energy was increased, which was consistent with the recently reported result for an electron interferometer. However, the lobe pattern and the sudden phase jump became less prominent. These results imply that the lobe pattern and the phase jump in an electron interferometer may be due to electron interactions inside the interferometer, as is predicted by the theory.

Is the Fano Antiresonance a Necessary Requirement for Circulating Currents in Mesoscopic Interferometers?

Yao Heng Su,Sam Young Cho,Ai Min Chen,Taeseung Choi 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.1

Coherent quantum tunneling effects on quantum interference are investigated in electron transport through a mesoscopic interferometer. An evanescent wave tunneling through a potential barrier in one arm can interfere with a propagating wave passing through the other arm of the interferometer. It is shown that, even for the same arm lengths, such a quantum interference can induce a circulating current, where Fano antiresonances do not occur in electron transmission. It is found that there exists a critical value of asymmetric arm lengths that gives rise to a Fano antiresonance in electron transmission for quantum interference between evanescent and propagating waves. We discuss the effects of Fano antiresonances originating from asymmetric arm lengths on circulating currents.

양자암호통신을 위한 비대칭 평판도파로 마이켈슨 간섭계

곽승찬,문형명,임기건,김진봉,조정식 한국물리학회 2018 새물리 Vol.68 No.7

We have designed and fabricated a planar lightwave circuit (PLC) Michelson interferometer device with a long delay path length for quantum cryptography. Faraday rotator mirrors were employed to improve the birefringence polarization effect in the asymmetric planar lightwave circuit, and a phase-modulated quantum cryptography system was constructed on the basis of the time-division interference scheme. The path difference in the present Michelson interferometer is 40.6 cm within a 0.2 mm error, and the excess loss is 1.56 dB. A quantum error rate of 2% was obtained from the quantum cryptography system utilizing the present asymmetric planar lightwave circuit interferometer. 양자암호통신을 위한 긴 지연 경로차를 갖는 평판도파로 마이켈슨 간섭계를 설계 제작하였다. 비대칭 도파로의 복굴절 편광 문제를 개선하기 위해 패러데이 거울(Faraday rotator mirror, FRM)을 반사경으로 사용하였고, 시분할 간섭 (time-division interference) 방식을 채택하여 위상변조 양자암호통신 시스템을 구성하였다. 제작된 마이켈슨 도파로 간섭계의 경로차는 40.6 cm이고, 광지연 길이의 편차가 0.2 mm 미만이며, 초과 손실은 1.56 dB 이다. 이 간섭계를 적용한 양자암호통신 시스템은 2%의 양자비트 오류율 값을 보여주었다.

Quenched Fano effect due to one Majorana zero mode coupled to the Fano interferometer

Qi Wang,Yu-Lian Zhu 한국물리학회 2018 Current Applied Physics Vol.18 No.11

We investigate the change of the Fano effect by considering one Majorana zero mode to couple laterally to the single-dot Fano interferometer. It is found that the Majorana zero mode quenches the Fano effect thoroughly and causes the conductance to be independent of the dot level, the dot-lead coupling, and the increase of the Majorana-dot coupling. As a result, the linear conductance becomes only related to the interlead coupling and the magnetic-flux phase factor. These results can be helpful for the detection of Majorana zero mode.

Performance Analysis of a High-Speed All-Optical Subtractor using a Quantum-Dot Semiconductor Optical Amplifier-Based Mach-Zehnder Interferometer

Mohammad Reza Salehi,Seyed Farhad Taherian 한국광학회 2014 Current Optics and Photonics Vol.18 No.1

This paper presents the simulation and design of an all-optical subtractor using a quantum-dot semiconductor optical amplifier Mach-Zehnder interferometer (QD-SOA MZI) structure consisting of two cascaded switches, the first of which produces the differential bit. Then the second switch produces the borrow bit by using the output of the first switch and the subtrahend data stream. Simulation results were obtained by solving the rate equations of the QD-SOA. The effects of QD-SOA length, peak power and current density have been investigated. The designed gate can operate at speeds of over 250 Gb/s. The simulation results demonstrate a high extinction ratio and a clear and wide-opening eye diagram.

ELECTRON TRANSPORT THROUGH A QUANTUM INTERFEROMETER WITH SIDE-COUPLED QUANTUM DOTS: A THEORETICAL STUDY

SANTANU K. MAITI 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2010 NANO Vol.5 No.4

We study electron transport through a quantum interferometer with side-coupled quantum dots. The interferometer, threaded by a magnetic flux φ, is attached symmetrically to two semi-infinite one-dimensional metallic electrodes. The calculations are based on the tight-binding model and the Green's function method, which numerically compute the conductance–energy and current–voltage characteristics. Our results predict that under certain conditions this particular geometry exhibits anti-resonant states. These states are specific to the interferometric nature of the scattering and do not occur in conventional one-dimensional scattering problems of potential barriers. Most importantly we show that, such a simple geometric model can also be used as a classical XOR gate, where the two gate voltages, viz, Va and Vb, are applied, respectively, in the two dots those are treated as the two inputs of the XOR gate. For φ = φ0/2 (φ0 = ch/e, the elementary flux-quantum), a high output current (1) (in the logical sense) appears if one, and only one, of the inputs to the gate is high (1), while if both inputs are low (0) or both are high (1), a low output current (0) appears. It clearly demonstrates the XOR gate behavior and this aspect may be utilized in designing an electronic logic gate.

Fano-Andreev Transport and Circulating Currents in Mesoscopic Interferometers

Yao Heng Su,Sam Young Cho 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.3

Quantum correlation and interference effects are investigated in mesoscopic interferometers connected to a normal metal and a superconductor. For quasiparticle excitation energies smaller than superconducting gap, a Fano-Andreev antiresonance for zero excitation energy is shown to be split into two zero-transmissions located at energies lower and higher than the Fano-Andreev antiresonance energy. For an excitation energy bigger than the gap, the higher energy antiresonance disappears for electron-like quasiparticle transport. In the presence of a superconductor interface potential <i>Z</i>, we find that the transport and the circulating currents normalized by their amplitudes for a clean interface have the same <i>I</i>(<i>Z</i>)-<i>Z</i> curve. We discuss a transition among the three types of normalized currents, which shows a characteristic transition diagram in association with the excitation energy. Also, as a demonstration of the existence of Andreev holes, we show that only the Andreev hole current can circulate along the interferometer loop.

Proposal for Locality Test of the Aharonov-Bohm E®ect via Andreev Interferometer without a Loop

강기천 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.9

We propose a quantitative test of the quantum locality in the electromagnetic interaction that generates the Aharonov-Bohm e®ect. For this purpose, we analyze the Lorentz-covariant ¯eld interaction approach based on the local action of gauge-invariant quantities only (\local" theory), and compare it with the standard potential-based (\nonlocal") theory. Whereas the two approaches yield identical results for topological phase and any phenomenon involving classical equation of motion, an example violating this equivalence is presented; interference of the Andreev re°ections from two independent superconducting inputs into a single normal metallic output. A well-de¯ned phase shift of the interference is predicted in the \local" theory. In contrast, the potential-based Lagrangian fails the corresponding prediction. This result is signi¯cant as it can settle the issue of quantum locality in the electromagnetic interaction.

Theoretically Exploring the Phase Precision in a Noisy Mach-Zehnder Interferometer

Xie Duan,Chen Haifeng 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.12

This paper presents the phase precision of a Mach-Zehnder interferometer in the presence of two types of quantum noise. Under the influence of amplitude-damping noise, the precisions of three input cases will gradually decrease and be less than the standard quantum limit. When the quantum states are influenced by bit-phase flip, the precisions for inputs of a coherent state and a squeezed vacuum state and the precision of spin squeezing state decrease at first and then increase with increasing (parameter characterizing the noise strength) from 0 to 1. Comparing the rates at which the precisions decrease, we found that the precision of the spin squeezing state decreased faster than those of the other two cases in most instances.