Abstract
Spectroscopy is a powerful tool to probe physical, chemical, and biological systems. Recent advances in microfabrication have introduced novel, intriguing mesoscopic quantum systems including superconductor-semiconductor hybrid devices and topologically non-trivial electric circuits. A sensitive, general purpose spectrometer to probe the energy levels of these systems is lacking. We propose an on-chip absorption spectrometer functioning well into the millimeter wave band which is based on a voltage-biased superconducting quantum interference device. We demonstrate the capabilities of the spectrometer by coupling it to a variety of superconducting systems, probing phenomena such as quasiparticle and plasma excitations. We perform spectroscopy of a microscopic tunable non-linear resonator in the 40-50 GHz range and measure transitions to highly excited states. The Josephson junction spectrometer, with outstanding frequency range, sensitivity, and coupling strength will enable new experiments in linear and non-linear spectroscopy of novel mesoscopic systems.
Highlights
Soon after the theoretical prediction of the Josephson effect, researchers directly measured microwave emission from a superconducting tunnel junction [1] and demonstrated that such junctions can be used as detectors of external radiation [2]
To demonstrate how Josephson spectroscopy can be useful in probing mesoscopic systems, in Fig. 4 we show the measured quasiparticle absorption spectrum of a short superconducting wire and the plasma resonance of a large Josephson junction
The low residual quasiparticle density in Josephson tunnel junctions leads to the high sensitivity and ultralow noise equivalent power (NEP)
Summary
Soon after the theoretical prediction of the Josephson effect, researchers directly measured microwave emission from a superconducting tunnel junction [1] and demonstrated that such junctions can be used as detectors of external radiation [2]. Deaver extended the technique to higher frequencies with a niobium point contact coated with a resonant absorber, measuring features in the current-voltage characteristic at 0.85 mV corresponding to the absorber frequency 416 GHz [4] Despite these early efforts coupling Josephson junctions to bulk samples, there have been few applications of the technique for spectroscopy of mesoscopic systems, artificial quantum coherent structures. Near half a flux quantum s ∼ 0/2, many photons couple to the DUT, and few excite the common mode [Fig. 1(b), red schematic], resulting in a current-voltage characteristic (IJ , VJ , s) with a large DUT absorption peak and little background signal at low voltages [Fig. 1(c), red, s = 0/2]. Changes in the shape of an absorption peak with increasing power reveal the anharmonicities typically found in mesoscopic systems
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