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arXiv:cond-mat/0410072 · Applied Physics Letters

Multiple junction biasing of superconducting tunnel junction detectors

K. Segall, J. J. Mazo, Terry P. Orlando

Published Apr 6, 2005• 2 citations
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Abstract

We describe a biasing scheme for single-photon detectors based on superconducting tunnel junctions. It replaces a single detector junction with a circuit of three junctions and achieves biasing of a detector junction at subgap currents without the use of an external magnetic field. This potentially increases the capability of these types of detectors and eases constraints in making large arrays. The biasing occurs through the nonlinear interaction of the three junctions, which we demonstrate through numerical simulation. This nonlinear state is numerically stable against external fluctuations and is compatible with high-fidelity electrical readout of the photon-induced current.

DOI
10.1063/1.1890467

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We describe a biasing scheme for single-photon detectors based on superconducting tunnel junctions. It replaces a single detector junction with a circuit of three junctions and achieves biasing of a detector junction at subgap currents without the use of an external magnetic field. This potentially increases the capability of these types of detectors and eases constraints in making large arrays. The biasing occurs through the nonlinear interaction of the three junctions, which we demonstrate through numerical simulation. This nonlinear state is numerically stable against external fluctuations and is compatible with high-fidelity electrical readout of the photon-induced current.
We present numerical simulations of a new biasing circuit for single photon detectors based on superconducting tunnel junctions. A single detector junction is replaced with a circuit of three junctions to achieve biasing of a detector junction at subgap currents without the use of an external magnetic field. The biasing occurs through the nonlinear interaction of the three junctions. We show nonlinear numerical simulation for different values of junction parameters and demonstrate that the biasing state is numerically stable against external fluctuations. The elimination of the external magnetic field potentially increases the capability of these types of photon detectors and eases constraints involved in the fabrication of large detector arrays.
Superconducting tunnel junctions (STJs) have been successfully used as single-photon detectors but require the use of a magnetic field to operate. A recent paper has proposed the idea to use a circuit of three junctions in place of a single junction in order to achieve the necessary biasing without applying a magnetic field. The nonlinear interaction between the different junctions in the circuit causes the existence of a stable subgap state for one of the junctions, which acts as the detector junction. In this paper, we present the first measurements demonstrating the existence of such a biasing state feasible for STJ detectors. Single junction measurements with an applied magnetic field help determine the functional form of the subgap current versus voltage; then the operating point of a three-junction circuit is measured and fit to theory. The excellent match between theory and experiment demonstrates the existence of the subgap biasing state. The outlook for possible use in detector applications is discussed.
Antenna-coupled superconducting tunnel junction detectors have the potential for photon-counting sensitivity at sub-mm wavelengths. The device consists of an antenna structure to couple radiation into a small superconducting volume and cause quasiparticle excitations, and a single-electron transistor to measure currents through tunnel junction contacts to the absorber volume. We will describe optimization of device parameters, and recent results on fabrication techniques for producing devices with high yield for detector arrays. We will also present modeling of expected saturation power levels, antenna coupling, and rf multiplexing schemes.
We present and theoretically analyze the performance of a nonlocal superconducting single-photon detector. The device operates due to the energy-to-phase conversion mechanism, where the energy of the absorbed single photon is transformed in a variation of the superconducting phase. Within this scope, the detector is designed in the form of a double-loop superconductor--normal-metal--superconductor (SSS-NNN-SSS) Josephson interferometer, where the detection occurs in a long SSS-NNN-SSS junction and the readout is operated by a short SSS-NNN-SSS junction. The variation of the superconducting phase across the readout junction is measured by recording the quasiparticle current flowing through a tunnel-coupled superconducting probe. By exploiting realistic geometry and materials, the detector is able to reveal single photons of frequency down to 10 GHz when operated at 10 mK. Furthermore, the device provides a value of the signal-to-noise ratio of up 104{10}^{4}104 in the range from 10 GHz to 10 THz by selection of the magnetic flux and the bias voltage. This device will hopefully find direct application as a single-photon detector in both basic science and quantum technology, while the energy-to-phase conversion mechanism could be the basis of nonlocal readout and memory architectures for superconducting qubits.
The magnetic field dependence of the Josephson current of a Josephson tunnel junction whose shape was a normal distribution is analyzed for superconducting tunnel junction (STJ) photon detector applications. It was found that the Josephson current of a normal distribution junction is very sensitive to the external magnetic field and follows a function of exp (-B 2), while a conventional rectangular STJ exhibits the well-known Fraunhofer pattern of sin x/x. Numerical calculations show that the Josephson current of the normal distribution junction can be suppressed by an external magnetic field that is one tenth of that needed for conventional rectangular junctions. Calculations of a normal distribution junction approximated with a 1 µm mesh also show that the Josephson current is sufficiently suppressed by a small magnetic field. The effect of the misalignment of the angle between the junction and the magnetic field was evaluated. It was found that for a normal-distribution-shaped junction, misalignment of the magnetic field is allowed within ± 5°, suppressing the Josephson effect by two orders of magnitude more than that of a rectangular junction.
Abstract Cascade multiplication is widely used to enhance photon detector sensitivity. While vacuum tube and semiconductor photomultipliers achieve high gains in the optical range, their performance at lower frequencies is limited by large work functions. Superconducting detectors overcome this constraint, enabling operation in the terahertz (THz) and microwave (MW) ranges. Here we introduce a concept of cascade-amplified superconducting detectors based on Josephson junction arrays. Interjunction coupling in an array triggers avalanche-like switching of multiple junctions upon photon absorption, resulting in cascade amplification of the readout voltage and an increased signal-to-noise ratio. We present prototypes using either low-T c linear Nb/NbxSi1−x/Nb arrays or Bi2Sr2CaCu2O8+δ high-T c stacked intrinsic Josephson junctions. Both MW and THz responses are analyzed and the advantages of the cascade detector over a conventional single-junction detector are demonstrated. Our findings suggest that Josephson junction arrays hold promise for the development of highly sensitive, broadband MW-to-THz detectors.