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Superconducting Photonics and Quantum Electronics

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Superconducting Photonics and Quantum Electronics

Dr. Kaveh Delfanazari 1,2

1 Electrical Engineering Division and 2 Semiconductor Physics Group, Cavendish Laboratory, University of Cambridge.

In this talk, I will present our recent research results on 1) Plasmonic Superconducting Metamaterials at Optical Wavelengths, and 2) Superconducting Quantum Electronics and THz Photonics:

1) Superconductors with strongly tunable superfluid plasma frequency, zero dc and low transient frequency losses present an opportunity for achieving metamaterials with extreme nonlinearity and tunability. To date all demonstration of these superconducting metamaterials have been reported in microwave, millimetre and THz waves. The response of such metamaterials has been tuned with incident light, magnetic fields, electrical current and temperature. I discuss the experimental observation of resonant response in the Niobium (Nb) superconducting metamaterial operating at optical wavelengths, i.e. above the superconducting gap. Our results show that, contrary to common wisdom, the extreme sensitivity of superconducting state to external perturbations, can be accessed in the optical range, thus paving the way for highly tunable optical metamaterials and plasmonic devices based on superconductors [1,2].

2) The intrinsic Josephson junctions (IJJs) in the high-Tc superconductor Bi2Sr2CaCu2O8+δ (Bi2212) are shown to have great potential for the construction of an oscillator emitting in the terahertz (THz) frequency regime. Single crystalline Bi2212 behaves as a stack of intrinsic Josephson junctions (IJJs), and has a large superconducting energy gap (100 meV). Bi2212 can generate EM waves with frequencies in the THz range (potentially between 0.3 and 15 THz) by the application of a dc-voltage V across the N active IJJs, each 1.533 nm thick, stacked along the c-axis of the mesa, with emission frequency f satisfying the quantum ac-Josephson relation f = fJ = (2e/h)V/N= 483.597891 GHz for V/N= 1 mV, where e is the electric charge and h is Planck’s constant. Although IJJ mesas are small in size, 100 um across and 1 um thick, they can generate high power THz waves at ~30 uW and the power generated by a three-mesa array was reported to be 610 uW. Thus, the IJJ -based THz emitter is one of the promising candidates to fill the THz gap with a compact, continuous-wave, active quantum solid state source. Advances that could lead to portable, battery-operated quantum THz devices will be discussed [3,4].

References: 1) K. Delfanazari, et al., and N. Zheludev, to be submitted. 2) R. Singh and N. Zheludev, Nat. Photonics, 8, 679 (2014). 3) K. Delfanazari, et al. IEEE Tran. THz Sci. and Technol. 5 (3) 505-511 (2015). 4) U. Welp, et al. Nat. Photonics, 7, 702 (2013).

This talk is part of the Semiconductor Physics Group Seminars series.

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