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Japanese Journal of Applied Physics

Current Doublers Based on the Quantum Current-Mirror Effect

Hiroshi Shimada, Sumio Hanadou, Takuma Kawai, Hiroto Kido, Yoshinao Mizugaki

Published Oct 1, 2008• 4 citations
Publisher

Abstract

Two types of current doublers, which operate in a sub-nanoampere range, have been fabricated as prototypes of a precise current multiplier for metrological application. The current doubling function of the devices is based on the quantum current-mirror effect in coupled arrays of small Josephson junctions. Both types of devices comprise three arrays of small Josephson junctions: the first device has two serial short arrays coupled to one long array, and the second device has three arrays of the same size arranged in parallel. The arrays for the current input are the long array in the first device and one of the three arrays in the second device, and a parallel connection of the other two arrays in each device forms the output port. In both types of devices, a current fed to the input array is doubled in the output circuit, which includes the connected arrays, up to about 100 pA with the accuracy ≤±3 pA, which is the uncertainty of the measurement system, by correlated tunnelings of Cooper-pair charge solitons in the arrays. The feasibility of producing a current multiplier has been ascertained on the basis of this effect.

DOI
10.1143/jjap.47.8131

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Two types of current doublers, which operate in a sub-nanoampere range, have been fabricated as prototypes of a precise current multiplier for metrological application. The current doubling function of the devices is based on the quantum current-mirror effect in coupled arrays of small Josephson junctions. Both types of devices comprise three arrays of small Josephson junctions: the first device has two serial short arrays coupled to one long array, and the second device has three arrays of the same size arranged in parallel. The arrays for the current input are the long array in the first device and one of the three arrays in the second device, and a parallel connection of the other two arrays in each device forms the output port. In both types of devices, a current fed to the input array is doubled in the output circuit, which includes the connected arrays, up to about 100 pA with the accuracy ≤±3 pA, which is the uncertainty of the measurement system, by correlated tunnelings of Cooper-pair charge solitons in the arrays. The feasibility of producing a current multiplier has been ascertained on the basis of this effect.
We report our observation of a current-multiplication trend in a new class of current-multiplier designs based on the quantum current-mirror effect in coupled arrays of small Josephson junctions. We demonstrate an extension of the current doubler device to 8- and 10-fold current multipliers by including additional Josephson junction arrays with simplified device geometry. The devices showed the expected current-multiplication trend at low temperatures where the charging effect was dominant. The magnitude of the current that exhibited such a multiplication trend was as large as 0.8 nA.
New types of followers and follower/doublers of DC voltage are proposed and analyzed. Operation of the devices is based on synchronization of the single-flux quantum (SFQ) pulses generated by overdamped Josephson junctions coupled by means of passive capacitive or inductive circuits. Two ways of combining the followers and doublers to get DC voltage multipliers and standards are described. Possible applications of these devices in A/D and D/A converters and RSFQ (rapid SFQ) logic circuits are also discussed. It is believed that the proposed multipliers and standards could produce stable output voltages in the 1-10 V range with output currents in the 0.1-1 mA range.>
The relationship between the coupling strength and the uncertainty in current duplication was investigated for the quantum current-mirror effect in capacitively coupled arrays of small Josephson junctions. With the increase in the coupling factor κ, defined as , with C c being the coupling capacitance and C the capacitance of the junction, the uncertainty decreased rapidly, especially at , and the standard deviation of the error reached as low as the order of 10 fA at . On this basis, we fabricated a 10-fold current multiplier composed of 11 simple arrays of junctions coupled more strongly ( ), using a plate-capacitor structure, than a previously studied multiplier ( ). It demonstrated more precise current-multiplication behavior than the previous multiplier with no intentional coupling structure, and the standard deviation of the error in current multiplication was decreased to less than 1/10 of the previous result.
This Thesis studies opportunities to create a quantum standard for the electric current with the help of tunnel junctions. We use two types of tunnel junctions: superconducting Josephson junctions, and NIS junctions where one of the electrodes is normal (N) and the other one superconducting (S). In both cases, tunnel junctions are employed in a single-electron transistor (SET) structure, which is used to transfer a controlled number k of electrons (e) with the repetition frequency f. The magnitude of the resulting current is thus I = kef. First, we study the Cooper pair sluice, where Josephson junctions are connected as two superconducting quantum interference devices (SQUID). A gate electrode is used to control the charge state of the superconducting island formed between the SQUIDs. The sluice is based on tuning the tunneling rates through the SQUIDs with local magnetic fluxes, which allows to control the direction of the charge transfer. Weak traces of current quantization can be observed up to above 1 nA, which is large enough current for many metrological purposes. However, the accuracy of the current is still far from what is required in metrology. We study also a new type of SQUID structure, the balanced SQUID, which could be used to improve the accuracy of the sluice or in, e.g., some quantum computing applications. Second, we employ NIS junctions in the hybrid (SINIS) single-electron transistor with superconducting leads and a normal-metal island. This structure can be used as the SINIS turnstile which lets electrons to flow one by one in the direction determined by the bias voltage. We report the first experimental results on the SINIS turnstile and two methods to improve the accuracy of the current: increasing the charging energy of the island or connecting the turnstile in a resistive environment. We also show that the SINIS turnstile can be used as an electronic radio-frequency refrigerator where tunneling processes cool the electron temperature of the normal-metal island.
A new type of followers and follower/doubles of dc voltages is suggested and analyzed. Operation of the devices is based on synchronization of the single flux quantum (SFQ) pulses (generated by overdamped Josephson junctions) by similar pulses in neighboring junctions coupled via passive capacitive or inductive circuits. Two ways of uniting the followers and doublers into dc voltage multipliers and standards are described. Possible applications of the new devices in A/D and D/A converters and RSFQ logic circuits are also discussed.
The output voltage of a rapid-single-flux-quantum digital-to-analog converter (RSFQ-DAC) is generated with a voltage multiplier (VM) that comprises multiple voltage mirror cells. We have demonstrated a new operation mode of a voltage mirror cell. It is a second-mode operation that doubles the input voltage, like the second-order Shapiro step. That is, a single cell works as a voltage doubler (VD). In this work, we propose a new parameter set of the VD (VD revision 1: VDr1) that improves the tolerance for multi-stage operation. Experimental results of a 16-stage VDr1 circuit are presented.