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Applied Physics Letters

Direct heterodyne detection of 245-GHz radiation using the internal narrowband oscillations of a resistive dc SQUID

J. M. V. Verschueren, A. A. Uiterwaal, Rob W. van der Heijden, P. Wyder

Published Feb 1, 1984• 0 citations
Publisher

Abstract

A current controlled voltage across a resistive section in a double Josephson junction interferometer (dc resistive superconducting quantum interference device) maintains a difference voltage between the junctions to generate a narrowband oscillatory signal at the beat frequency νq of the individual junction frequencies. This internal oscillation was used to directly down-convert a signal at 246 GHz to a very low (<1 MHz) intermediate frequency.

DOI
10.1063/1.94724

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Applied Physics Letters•Mar 27, 2000•14 citations
A current controlled voltage across a resistive section in a double Josephson junction interferometer (dc resistive superconducting quantum interference device) maintains a difference voltage between the junctions to generate a narrowband oscillatory signal at the beat frequency νq of the individual junction frequencies. This internal oscillation was used to directly down-convert a signal at 246 GHz to a very low (<1 MHz) intermediate frequency.
The output voltage of a dc superconducting quantum interference device (SQUID) containing a resistive section Rs oscillates at a frequency νq =Vs/ φ0 (φ0=flux quantum) when a current controlled voltage Vs is maintained across Rs. These oscillations have been observed from ∼10−1 to 1011 Hz, using Rs values ranging from ∼10−10 to ∼10−3 Ω in low inductance (∼10−10 H) point contact SQUID loops. At high frequencies, they manifest themselves in the dc current-voltage characteristics by inducing extra current steps.
An all thin-film resistive SQUID with two Josephson tunnel junctions has been designed, fabricated and studied. As well as the two junctions, this device consists of a low ohmic (1.9*10 -6 Omega ) resistive part connected by superconducting leads to both junctions in a loop with very low ( approximately 10 -11 H) inductance. A direct current flowing through the resistive part fixes the voltage difference between the two Josephson junctions that are additionally fed by a bias current. The voltage difference is converted into a signal frequency that can be picked up from the SQUID with a conversion factor of ( phi o ) -1 =483.6 MHz mu V -1 , defined only by the electron charge and Planck's constant. An output signal level (peak-to-peak) of about 50 mu V has been obtained. The low frequency range (below 100 kHz) of the output signal frequency has been investigated. The possibilities of considerably extending this frequency range are also discussed.
We describe a new dc-superconducting quantum interference device (SQUID) circuit of the FM type, which has a large coefficient for converting an applied magnetic flux into a frequency of MHz band or a lower band. The circuit consists of a SQUID amplifier composed of two stages, formed by a superconducting weak link and two dc-SQUID elements with nonhysteretic characteristics. In the first stage, the weak link and dc-SQUID elements are connected in parallel and operated by a common bias voltage. Since the respective elements oscillate with high frequencies by the ac Josephson effect, the two frequencies interact with each other, so that, the first stage generates a beat signal of a lower frequency. In the second stage, the other dc-SQUID element with a intrinsic flux gain enhances the beat signal generated during the first stage. A theoretical analysis of the circuit with computer simulation shows that the beat frequency is a periodical function of the magnetic flux, and the SQUID amplifier with two stages can improve the flux sensitivity.
Experimental evaluation of a high-temperature superconducting Josephson heterodyne mixer based on a 'resistive-SQUID' configuration is reported. The device consists of two YBa 2 Cu 3 O 7− x step-edge Josephson junctions connected via a small resistor in an otherwise superconducting loop. It has been previously shown to generate a heterodyne oscillation, which is frequency-tunable by a control current through the resistor. Under certain conditions, this device can operate as a frequency-tunable heterodyne mixer (down-converter) in the presence of an RF signal. In this paper, we describe the operation of the autonomous Josephson mixer–local oscillator device and present the experimental results on the mixer performances in terms of the junction current–voltage characteristics, the frequency tunability, linearity, and dynamic range as well as their temperature dependence for signal frequencies from 1 to 5 GHz.
A pair of high-temperature-superconducting (HTS) step-edge Josephson junctions connected in the ‘resistive-SQUID’ (R-SQUID) configuration has been previously shown to generate a heterodyne oscillation which is frequency-tunable by a control current across the resistor. A method is described which enables the R-SQUID to act both as the local oscillator (LO) and simultaneously as a radio- frequency down-converter element. For the first time the autonomous Josephson mixer–local oscillator device for signal frequencies between 1–5 GHz, over a temperature range of 20–70 K, is demonstrated.
High-temperature-superconducting (HTS) resistively shunted superconducting quantum interference devices, consisting of two yttrium–barium–copper–oxide (YBCO) grain boundary junctions shunted by gold-film resistors of ∼20 μΩ, have been prepared and characterized at temperatures from 17 to 74 K. The small value and stability of the resistor allows narrow-band heterodyne oscillations to be generated between the Josephson oscillations in the individual junctions. The frequency can be precisely controlled in accordance with the ac Josephson effect by adjustment of an external current applied to the YBCO–Au–YBCO shunt resistor, and the linewidth is determined in principle only by Johnson noise in the resistor. Off-chip detection and spectral analysis of the heterodyne signal generated in this way has not been previously reported. Measurements of the signal power (∼nW), the tunability of the center frequency from 5 to 50 MHz, the frequency stability and the linewidth of the heterodyne Josephson oscillation are described. Although linewidth broadening due to nonthermal fluctuations is observed, the linewidth of ∼30 kHz at T=17 K, at a center frequency of 24 MHz, is believed to be the narrowest reported for Josephson oscillations in an HTS device of this type.