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

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

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

Guiding of Terahertz Photons in Superconducting Nano-Circuits

The field of plasmonics, as one of the fascinating areas of photonics, has received great attention for its capability of deep subwavelength confinement. We present a nanoscale plasmonic slot waveguide based on high transition temperature (T c ) superconductor Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO). The effect of geometrical parameters on the modal properties of the BSCCO plasmonic slot waveguide and the thermal tuning of the modal properties of the waveguide are explored. It is shown that the rising of temperature results in increasing the mode effective refractive index in exchange for decreasing the propagation length of surface plasmon polaritons (SPPs). Our proposed plasmonic waveguide paves the way for the development of the BSCCO based THz photonic integrated circuity at the nanoscale

Engineering ultrastrong coupling between Josephson plasmon polaritons and subwavelength microcavity arrays in silicon: van der Waals layered superconductor heterostructure for terahertz hybrid circuit cavity quantum electrodynamics

The realisation of the ultrastrong coupling between Josephson plasma waves (JPWs) and terahertz (THz) photons in the sub-wavelength microcavity array is of interest for manipulating the THz cavity quantum electrodynamics, ultra-high-resolution sensing and imaging, and quantum information processing. Here, we propose ultrastrong light-matter interactions in a deeply subwavelength microcavity array based on hybrid silicon and high-temperature (Tc) superconducting (HTS) BSCCO van der Waals (vdWs) heterostructure. We describe Josephson THz cavity electrodynamics and ultrastrong coupling process between THz radiation and the JPWs in Josephson medium which is naturally present in BSCCO vdWs. The resonance frequency of microcavities is swept through the Josephson plasma frequency by altering their width. THz reflection demonstrates the anti-crossing behaviour of ultrastrong coupling with a normalized Rabi frequency (coupling strength) 2R/fc = 0.29 for the BSCCO thickness t= 200 nm, which increases to the value of 0.87 for t= 800 nm. Furthermore, the thermal behaviour of coupling strength shows modulation of Rabi splitting 2R with temperature. We show that the normalized Rabi splitting 2R/fc is independent of the temperature in the BSCCO superconducting regime, while a weak coupling can be observed above the superconducting transition temperature. Our results shall guide the effort in the development of power-efficient coherent THz sources, sensitive detectors, and tunable bolometers based on BSCCO HTS quantum materials

Engineering ultrastrong coupling between Josephson plasmon polaritons and subwavelength microcavity arrays in silicon/van der Waals layered superconductor heterostructure for terahertz hybrid circuit cavity quantum electrodynamics

The realization of the ultrastrong coupling between Josephson plasma waves (JPWs) and terahertz (THz) photons in the subwavelength microcavity array is of interest for manipulating the THz cavity quantum electrodynamics (cQED), ultrahigh-resolution sensing and imaging, and quantum information processing. Here, we describe the engineering of ultrastrong light-matter interactions in a deeply subwavelength microcavity array based on the hybrid silicon and high-temperature superconductor (HTS) Bi2Sr2CaCu2O8+δ (BSCCO) van der Waals (vdW) heterostructure. We perform numerical modeling and analytical calculation to describe Josephson THz cQED and the ultrastrong coupling process between THz radiation and the JPWs in Josephson medium which is naturally present in BSCCO vdW. The resonance frequency of microcavities is swept through the Josephson plasma frequency by altering their width. THz reflection demonstrates the anticrossing behavior of ultrastrong coupling with a normalized Rabi frequency (coupling strength) 2ωR/fc=0.29 for the BSCCO thickness t=200 nm, which increases to the value of 0.87 for t=800 nm. Furthermore, the thermal behavior of coupling strength shows modulation of Rabi splitting 2ωR with temperature. We show that the normalized Rabi splitting 2ωR/fc is independent of the temperature in the BSCCO superconducting regime, while a weak coupling can be observed above the superconducting transition temperature. The proposed chip-scale THz photonic integrated circuit with subwavelength microcavity metamaterial array shall guide the effort in the development of power-efficient coherent THz sources, quantum sensors, ultrasensitive detectors, parametric amplifiers and tunable bolometers based on BSCCO HTS quantum material.</p

Research Data supporting ''Millimeter wave to terahertz compact and low-loss superconducting plasmonic waveguides for cryogenic integrated nano-photonics''

Origin and MATLAB can be used to plot the files. “Figure2” contains the effective refractive index, propagation distance, and mode confinement at different gap heights for different gap widths” (BOOK1). “Figure3” includes the effective refractive index, propagation distance, and mode confinement of THz plasmonic waveguide at different frequencies as a function of temperature (BOOK1), and the permittivity of the superconducting thin film at different frequencies as a function of temperature (BOOK2). “Figure4” contains the dispersion curve of the THz plasmonic waveguide for different temperatures as well as light line dispersion (BOOK1), and electric field distribution above the waveguide in different temperatures (BOOK2). “Figure A1” contains the mode confinement and propagation distance as a function f temperature for superconducting and gold plasmonic waveguides (BOOK1). “Figure A2” contains the absorption coefficient of superconducting plasmonic waveguides as a function of temperature at different frequencies (BOOK1), and the absorption coefficient of the gold plasmonic waveguide as a function of frequency (BOOK2). For full theoretical calculation, please refer to the main publication