Hypersensitive Tunable Josephson Escape Sensor for Gigahertz Astronomy

Abstract

Single-photon detectors and bolometers represent the bridge between different topics in science, such as quantum computation, astronomy, particle physics, and biology. Nowadays, superconducting bolometers and calorimeters are the most-sensitive detectors in the terahertz and subterahertz bands. Here, we propose and demonstrate a Josephson escape sensor (JES) that could find natural application in astrophysics. The JES is composed of a fully superconducting one-dimensional Josephson junction, whose resistance-versus-temperature characteristics can be precisely controlled by a bias current. Therefore, differently from traditional superconducting detectors, the JES sensitivity and working temperature can be in situ simply and finely tuned depending on the application requirements. A JES bolometer is expected to show an intrinsic thermal-fluctuation-noise noise-equivalent power on the order of 10 −25 W/Hz 1/2 , while a JES calorimeter could provide a frequency resolution of about 2 GHz, as deduced from the experimental data. In addition, the sensor can operate at the critical temperature (i.e., working as a conventional transition-edge sensor), with a noise-equivalent power of approximately 6 × 10 −20 W/Hz 1/2 and a frequency resolution of approximately 100 GHz.

Fully Superconducting Josephson Bolometers for Gigahertz Astronomy

“…The magnetic field generated at the wire surface by the maximum possible bias current is B I,max = µ 0 I C,0 /(2πt) 5 µT. This value is orders of magnitude lower than the critical magnetic field of A that was measured to be about 21 mT [34]. Therefore, the self generated magnetic field does not affect the properties of the device.…”

“…Notably, the current bias modulates the device sensitivity over about 6 orders of magnitude. Furthermore, the extracted data indicate that the JES [34] reaches best sensitivities several orders of magnitude better than nano-TES bolometers [33] and all other sensors proposed and realized [16][17][18][19][20][21][22][26][27][28][29][30][31][32][35][36][37]48] so far. Specifically, the JES showed unprecedented values of NEP TFN,JES as low as ∼1 × 10 −25 W/ √ Hz for the highest bias current I = 370 nA (I C,0 /I 1.5) corresponding to a working temperature of about 18 mK.…”

“…The sensors presented in this review, i.e., the nano-TES [33] and the JES [34], can be described as a 1D fully superconducting Josephson junction (1D-JJ). A 1D-JJ is realized in the form of a superconducting nanowire (A), with both lateral dimensions (thickness (t) and width (w)) smaller than its coherence length (ξ A ) and the London penetration depth of the magnetic field (λ L,A ), separating two superconducting lateral banks (B), as schematically shown in Figure 2a.…”

“…Instead, we review recent developments of superconducting radiation sensors based on a structure that shares many technological aspects with the already employed TESs and KIDs. Indeed, the nanoscale transition edge sensor (nano-TES) [33] and the Josephson escape sensor (JES) [34] are envisioned by downsizing the active region of a TES to the nano-scale. In particular, they employ a one dimensional fully superconducting Josephson junction (1D-JJ) as radiation absorber.…”

“…Moreover, the nano-TES and JES intrinsic values of NEP were deduced from the transport and thermal data. The nano-TES is predicted to show a thermal fluctuation limited NEP of about 5 × 10 −20 W/ √ Hz [33], while the JES is expected to provide an NEP of the order of 10 −25 W/ √ Hz [34]. As a consequence, these sensors could be the basis of detectors pointing towards unprecedented sensitivities in the GHz and THz bands.…”