Evidence for Majorana phases in the magnetoconductance of topological junctions based on two-dimensional electron gases

We calculate the linear conductance of a two-dimensional electron-gas-based junction between a normal semiconductor section and a hybrid semiconductor-superconductor section, under perpendicular magnetic field. We consider two important terms often neglected in the literature, the magneto-orbital and transverse Rashba spin-orbit. The strong orbital effect due to the magnetic field yields topological phase transitions to nontrivial phases hosting Majorana modes in the hybrid section. The presence of a potential barrier at the junction interface reveals the Majorana phases as quantized plateaus of high conductance, for low values of the chemical potential. In wide junctions (or large chemical potentials) the phase transitions occur at low magnetic fields but the magneto-conductance becomes anomalous and lacks clearly quantized plateaus

Integrated, portable, tunable, and coherent terahertz sources and sensitive detectors based on layered superconductors

Current compact emitter and receiver technologies are generally inefficient and impractical at terahertz (THz) frequencies between 0.1 and 10 THz. Hence, a gap exists between mature microwave and developed optical technologies. On-chip, integrated broadly tunable and powerful quantum sources that coherently radiate THz waves between 0.1 and 11 THz (potentially extendable to 15 THz) and with potential output power of >1 mW can be achieved based on quantum tunneling of electron pairs across the stack of intrinsic Josephson junctions (IJJs) naturally present in a single crystal of the layered high-Tc superconducting Bi2Sr2CaCu2O8+δ (BSCCO). Such devices have been found to be especially promising solid-state THz sources capable of bridging the entire THz gap, as their wide-frequency tunability range is superior to that obtained from their semiconducting-based rivals, either single resonant-tunneling diodes (RTDs) or THz-quantum cascade lasers (QCLs). Due to the unique electrodynamics of BSCCO, they can also be operated as switching current detectors, paving the way for the realization of on-chip THz-integrated circuits for applications in ultrahigh-speed telecommunications, quantum information, on-chip spectroscopy, and nondestructive sensing, testing, and imaging. This article reviews the history and recent advances in THz sources and detectors based on IJJs with a focus on the application of IJJ THz devices in THz spectroscopy and various types of THz imaging systems such as reflection, transmission, and computed tomography. We show that compact IJJ THz devices with sub-centimeter-sized modules are easy to use in many applications, as they can be regarded as pocket quantum THz torches

Millimeter-Wave-to-Terahertz Superconducting Plasmonic Waveguides for Integrated Nanophotonics at Cryogenic Temperatures.

Plasmonics, as a rapidly growing research field, provides new pathways to guide and modulate highly confined light in the microwave-to-optical range of frequencies. We demonstrated a plasmonic slot waveguide, at the nanometer scale, based on the high-transition-temperature (Tc) superconductor Bi2Sr2CaCu2O8+δ (BSCCO), to facilitate the manifestation of chip-scale millimeter wave (mm-wave)-to-terahertz (THz) integrated circuitry operating at cryogenic temperatures. We investigated the effect of geometrical parameters on the modal characteristics of the BSCCO plasmonic slot waveguide between 100 and 800 GHz. In addition, we investigated the thermal sensing of the modal characteristics of the nanoscale superconducting slot waveguide and showed that, at a lower frequency, the fundamental mode of the waveguide had a larger propagation length, a lower effective refractive index, and a strongly localized modal energy. Moreover, we found that our device offered a larger SPP propagation length and higher field confinement than the gold plasmonic waveguides at broad temperature ranges below BSCCO's Tc. The proposed device can provide a new route toward realizing cryogenic low-loss photonic integrated circuitry at the nanoscale

Integrated, portable, tunable, and coherent terahertz sources and sensitive detectors based on layered superconductors

Current compact emitter and receiver technologies are generally inefficient and impractical at terahertz (THz) frequencies between 0.1 and 10 THz. Hence, a gap exists between mature microwave and developed optical technologies. On-chip, integrated broadly tunable and powerful quantum sources that coherently radiate THz waves between 0.1 and 11 THz (potentially extendable to 15 THz) and with potential output power of >1 mW can be achieved based on quantum tunneling of electron pairs across the stack of intrinsic Josephson junctions (IJJs) naturally present in a single crystal of the layered high-T c superconducting Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO). Such devices have been found to be especially promising solid-state THz sources capable of bridging the entire THz gap, as their wide-frequency tunability range is superior to that obtained from their semiconducting-based rivals, either single resonant-tunneling diodes (RTDs) or THz-quantum cascade lasers (QCLs). Due to the unique electrodynamics of BSCCO, they can also be operated as switching current detectors, paving the way for the realization of on-chip THz-integrated circuits for applications in ultrahigh-speed telecommunications, quantum information, on-chip spectroscopy, and nondestructive sensing, testing, and imaging. This article reviews the history and recent advances in THz sources and detectors based on IJJs with a focus on the application of IJJ THz devices in THz spectroscopy and various types of THz imaging systems such as reflection, transmission, and computed tomography. We show that compact IJJ THz devices with sub-centimeter-sized modules are easy to use in many applications, as they can be regarded as pocket quantum THz torches

Thermal tuning of high-Tc superconducting Bi2Sr 2CaCu2 O8+δ terahertz metamaterial

We introduce a class of low-loss subwavelength resonators and report the first demonstration of a high-temperature ( Tc ) superconducting Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) terahertz (THz) metamaterial. The numerical simulations and analytical calculations are performed to study the electromagnetic response of the subwavelength BSCCO split-ring resonators (SRRs) to the incident photons with energies below the superconducting gap energy. A transition of resonance strength is observed as a dip in resonance frequency for temperatures below BSCCO Tc . To interpret the transmission spectra, resonance switching, and frequency tuning of SRRs, we calculate the temperature dependent complex permittivity and surface impedance of a 200 nm thick unpatterned slightly underdoped BSCCO thin film. We compare the resonance tunability of SRRs made of the extremely disorder superconductor (BSCCO) with metamaterials made of a weakly disorder superconductor YBa 2 Cu 3 O 7 (YBCO) and show that the resonance quality and frequency tuning are comparable for these two metamaterials. Our results may be useful for THz emitters and detectors developments, for instance, by integration of SRRs with BSCCO THz emitters and microstrip antennas, the device functionalities such as polarization, emission pattern directivity, and output power could be controlled and improved

Cavity mode enhancement of terahertz emission from equilateral triangular microstrip antennas of the high-TcT_c superconductor Bi2_2Sr2_2CaCu2_2O8+δ_{8 + δ}

We study the transverse magnetic (TM) electromagnetic cavity mode wave functions for an ideal equilateral triangular microstrip antenna (MSA) exhibiting $C_{3v}$ point group symmetry. When the $C_{3v}$ operations are imposed upon the antenna, the TM($m,n$) modes with wave vectors $\alpha \sqrt[ ]{m^2 + nm + n^2}$ are much less dense than commonly thought. The $R_3$ operations restrict the integral $n$ and $m$ to satisfy $\mid m - n \mid$ = 3$p$, where $p \geq$ 0 and $p \geq$ 1 for the modes even and odd under reflections about the three mirror planes, respectively. We calculate the forms of representative wave functions and the angular dependence of the output power when these modes are excited by the uniform and non-uniform ac Josephson current sources in thin, ideally equilateral triangular MSAs employing the intrinsic Josephson junctions in the high transition temperature $T_c$ superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8 + \delta}$, and fit the emissions data from an earlier sample for which the $C_{3v}$ symmetry was apparently broken.UCF RAMP program, JSPS Research Fellowship for young scientists, CREST-JST (Japan Science and Technology Agency), WPI (World Premier International Research Center Initiative)- MANA (Materials Nanoarchitectonics) project (NIMS

Characterizing Niobium Nitride Superconducting Microwave Coplanar Waveguide Resonator Array for Circuit Quantum Electrodynamics in Extreme Conditions

The high critical magnetic field and relatively high critical temperature of niobium nitride (NbN) make it a promising material candidate for applications in superconducting quantum technology. However, NbN-based devices and circuits are sensitive to decoherence sources such as two-level system (TLS) defects. Here, we numerically and experimentally investigate NbN superconducting microwave coplanar waveguide resonator arrays, with a 100 nm thickness, capacitively coupled to a common coplanar waveguide on a silicon chip. We observe that the resonators' internal quality factor (Qi) decreases from Qi ~ 1.07*10^6 in a high power regime ( = 27000) to Qi ~ 1.36 *10^5 in single photon regime at temperature T = 100 mK. Data from this study is consistent with the TLS theory, which describes the TLS interactions in resonator substrates and interfaces. Moreover, we study the temperature dependence internal quality factor and frequency tuning of the coplanar waveguide resonators to characterise the quasiparticle density of NbN. We observe that the increase in kinetic inductance at higher temperatures is the main reason for the frequency shift. Finally, we measure the resonators' resonance frequency and internal quality factor at single photon regime in response to in-plane magnetic fields B||. We verify that Qi stays well above 10^4 up to B|| = 240 mT in the photon number = 1.8 at T = 100 mK. Our results may pave the way for realising robust microwave superconducting circuits for circuit quantum electrodynamics (cQED) at high magnetic fields necessary for fault-tolerant quantum computing, and ultrasensitive quantum sensing

Active Terahertz Modulator and Slow Light Metamaterial Devices with Hybrid Graphene-Superconductor Photonic Integrated Circuits.

Metamaterial photonic integrated circuits with arrays of hybrid graphene-superconductor coupled split-ring resonators (SRR) capable of modulating and slowing down terahertz (THz) light are introduced and proposed. The hybrid device's optical responses, such as electromagnetic-induced transparency (EIT) and group delay, can be modulated in several ways. First, it is modulated electrically by changing the conductivity and carrier concentrations in graphene. Alternatively, the optical response can be modified by acting on the device temperature sensitivity by switching Nb from a lossy normal phase to a low-loss quantum mechanical phase below the transition temperature (Tc) of Nb. Maximum modulation depths of 57.3% and 97.61% are achieved for EIT and group delay at the THz transmission window, respectively. A comparison is carried out between the Nb-graphene-Nb coupled SRR-based devices with those of Au-graphene-Au SRRs, and significant enhancements of the THz transmission, group delay, and EIT responses are observed when Nb is in the quantum mechanical phase. Such hybrid devices with their reasonably large and tunable slow light bandwidth pave the way for the realization of active optoelectronic modulators, filters, phase shifters, and slow light devices for applications in chip-scale future communication and computation systems