Radio-frequency (RF) to direct current (DC) converter and bipolar quantized supercurrent generator (QSG)

#The currently claimed embodiments of the present invention relate to quantum computation, and more specifically, to a radio-frequency (RF) to direct current (DC) converter and bipolar quantized supercurrent generator (QSG) and quantum mechanical systems using the same.

#The application of fast flux bias pulses has traditionally been accomplished by room temperature giga samples per second (GS/s) digital-to-analog converters (DACs) driving current into temperature T=4K resistors with the precision of the pulse amplitude set by a number of DAC bits and the Johnson noise of the bias resistor. However, this method suffers from large pulse shape distortion as the current pulse must traverse multiple temperature stages and filtering before arriving at the intended device (device under test—DUT). Additionally, to achieve precise pulse heights, a voltage DAC with a relatively large count is required. Furthermore, the wiring required to bias a plurality n of devices scales linearly with the number n of the plurality of devices. Therefore, it is desirable to provide a new way or system to generate fast current pulses that can either be applied directly to the device (DUT) or coupled as a flux via a pair of mutual inductors.

#In addition, the application of static flux bias to superconducting circuitry has predominantly been performed via the application of a voltage to a cold resistor (e.g., at a temperature T of about 4K) which then drives current to a primary inductance loop mutually coupled to a device (DUT). The scaling of this approach in terms of the room temperature wiring and voltage source overhead is linear in the number of devices (DUTs) one wishes to flux bias. The heat load and physical space required to accommodate hundreds if not thousands of physical devices (e.g., qubits) required to demonstrate quantum advantage via implementation of computing paradigms such as the surface code is untenable. Therefore, it is also desirable to provide a new way or system to generate bi-polar flux bias current such that the scaling in number of devices to room temperature control lines is improved while achieving minimal to zero dynamic heat load at any stage of the cryostat.

#The present disclosure, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

#FIG. 1 is a schematic electronic circuit of a radio-frequency (RF) to direct current (DC) converter, according to an embodiment of the present invention;

#FIG. 2 is a plot of a resultant Current-Voltage for a simulation (for example, using WRSpice) of a 20 JJs (e.g., feeding Josephson transmission line—FJTL) for different drive frequencies (frequencies shown are 5 GHz, 7 GHz, 9 GHz, 11 GHz, 13 GHz, and 15 GHz), according to an embodiment of the present invention;

#FIG. 1 is a schematic electronic circuit of a radio-frequency (RF) to direct current (DC) converter, according to an embodiment of the present invention. The radio-frequency (RF) to direct current (DC) converter 100 includes a direct electrical current (DC) input port 102 and a radiofrequency (RF) input port 104. The converter 100 also includes a direct electrical current (DC) to single flux quantum (SFQ) (DC/SFQ) converter 106 connected to the RF input port 104. The DC to SFQ converter 106 is configured to convert RF current to SFQ current pulses. The radio-frequency (RF) to direct current (DC) converter 100 also includes a Josephson junction (JJ) 108A connected to both the DC input port 102 via a first induction line 110 and to the DC to SFQ converter 106 via a second induction line 112 and to ground 114. The converter 100 also includes a resistor 118 connected to the Josephson junction (JJ) 108A and to the DC input port 102 via a third induction line 120.

#In operation, when a DC electrical current is applied via the DC input port 102, the DC electrical current is shunted to ground 116 through the JJ 108A and substantially no DC electrical current flows through the resistor 118, and when an RF electrical current is applied via the RF input port 104, output trains of SFQ current pulses from the DC to SFQ converter 106 with pulse-to-pulse spacing inversely proportional to the RF electrical current frequency cause the Josephson junction (JJ) 108A to switch at a rate commensurate with an RF frequency of the RF electrical current to generate a steady state voltage across the Josephson junction (JJ) 108A linearly dependent on the RF frequency such that an electrical current flowing through the resistor 118 is directly dependent on the RF frequency of the RF electrical current.

#In an embodiment, the converter 100 further includes a plurality of Josephson junctions 108A, 108B, 108C, 108D connected to both the DC input port 102 via the first induction line 110 and to the RF input port 104 via the DC to SFQ converter 106 through the second induction line 112 and to ground 116. Although four Josephson junctions are depicted in FIG. 1, as it can be appreciated any number of Josephson junctions can be used, for example, two, three or more. The plurality of Josephson junctions 108A, 108B, 108C, 108D are configured to switch, when the RF electrical current is applied via the RF input port 104, at a rate commensurate the RF frequency of the RF electrical current to generate a steady state voltage across the plurality of Josephson junctions (JJ) 108A, 108B, 108C, 108D linearly dependent on the RF frequency such that the electrical current flowing through the resistor 118 is directly dependent on the RF frequency of the RF electrical current. It might be worth noting that the more JJs used in the FJTL, the greater the amount of current the FJTL can source was driven with RF.