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

Abstract

A radio frequency (RF) to direct current (DC) converter is provided. When a DC current is applied via a DC input port of the converter, the DC current is shunted through a Josephson junction (JJ) of the converter to ground and substantially no DC current flows through a resistor of the converter, and when an RF current is applied via an RF input port of the converter, a sequence of SFQ current pulses is output from a DC to SFQ converter of the RF to DC converter, the sequence of SFQ current pulses having a pulse to pulse interval inversely proportional to a frequency of the RF current causes the JJ to switch at a rate commensurate with an RF frequency of the RF current to generate a steady state voltage across the JJ dependent on the RF frequency.

Description

Technical Field

[0001] The currently claimed embodiments of the present invention relate to quantum computing, and more specifically to radio frequency (RF) to direct current (DC) converters and dual-polarization supercurrent generators (QSGs) and quantum mechanical systems using them. Background Technology

[0002] Traditionally, the application of fast flux bias pulses has been accomplished by driving current to a 4K resistor at temperature T using a room-temperature gigabit samples per second (GS / s) digital-to-analog converter (DAC). This resistor has the accuracy of the pulse amplitude set by the Johnson noise of the multiple DAC bits and the bias resistor. However, this method suffers from large pulse shape distortion because the current pulse must traverse multiple temperature stages and be filtered before reaching the intended device (DUT). Furthermore, a relatively large voltage count is required for the DAC to achieve accurate pulse height. Additionally, the wiring required to bias multiple n devices scales linearly with the number of devices, n. Therefore, it is desirable to provide a new method or system for generating fast current pulses that can be applied directly to the device (DUT) or coupled into flux via a pair of current transformers.

[0003] Furthermore, applying static flux bias to superconducting circuits is primarily performed by applying a voltage to a cold resistor (e.g., at a temperature T of approximately 4 K), which then drives the current to the primary inductance loop interconnected to the device under test (DUT). The scaling of this approach in terms of room-temperature wiring and voltage source overhead is linear with respect to the number of devices (DUTs) for which flux bias is desired. The thermal load and physical space required to accommodate hundreds (if not thousands) of physical devices (e.g., qubits) needed to demonstrate quantum advantage via computational paradigms (e.g., surface codes) are infeasible. Therefore, it is also desirable to provide a novel method or system for generating bipolar flux bias currents that improves the scaling of the number of devices with respect to the room-temperature control line while achieving minimal to zero dynamic thermal load at any stage of the cryostat. Summary of the Invention

[0004] An aspect of the present invention is to provide a radio frequency (RF) to direct current (DC) converter, including a direct current (DC) input port; an RF input port; and a direct current (DC) to single-flux quantum (SFQ) converter connected to the RF input port, the DC to SFQ converter being configured to convert RF current into SFQ current pulses. The converter further includes a Josephson junction (JJ) connected to the DC input port via a first inductive line and connected to the DC to SFQ converter via a second inductive line, and grounded; and a resistor connected to the Josephson junction via a third inductive line and connected to the DC input port. In operation, when a DC current is applied via the DC input port, the DC current is shunt to ground through the JJ, and substantially no DC current flows through the resistor. When an RF current is applied via the RF input port, the output sequence of SFQ current pulses from the DC-to-SFQ converter, having a pulse-to-pulse interval inversely proportional to the frequency of the RF current, causes the Josephson junction (JJ) to switch at a rate commensurate with the RF frequency of the RF current, thereby linearly generating a steady-state voltage across the Josephson junction (JJ) depending on the RF frequency, such that the current flowing through the resistor is directly dependent on the RF frequency of the RF current.

[0005] In one embodiment, the converter further includes a plurality of Josephson junctions connected to the DC input port via the first inductive line and connected to the RF input port via the second inductive line through the DC-to-SFQ converter, and grounded. The plurality of Josephson junctions are configured to switch at a rate proportional to the RF frequency of the RF current when the RF current is applied via the Sohu RF input port, to generate a steady-state voltage across the plurality of Josephson junctions (JJs) depending on the RF frequency, such that the current flowing through the resistor is directly dependent on the RF frequency of the RF current.

[0006] In an embodiment, the steady-state voltage (V) across the Josephson junction (JJ) is related to the RF frequency (f) according to the following equation. clk Proportional: V=Φ0x f clk , where Φ0 is the superconducting magnetic flux quantum.

[0007] Another aspect of the present invention is to provide a quantum mechanical system including the aforementioned radio frequency (RF) to direct current (DC) converter. In one embodiment, the quantum mechanical system further includes at least one quantum mechanical device connected to the resistor. In one embodiment, the one or more devices include, for example, qubits, superconducting quantum interference devices, or non-quantum mechanical circuits.

[0008] In one embodiment, the quantum mechanical system further includes a fast single-throughput quantum (RSFQ) pulse multiplier having an input port and an output port. The output port of the RSFQ pulse multiplier is connected to the input port of the DC-to-SFQ converter, and the RSFQ pulse multiplier is configured to generate an SFQ pulse current input through the input port of the DC-to-SFQ converter.

[0009] In one embodiment, the RSFQ pulse multiplier is configured to generate multiple current pulses at twice the rate of an SFQ pulse applied at the output port of the RSFQ pulse multiplier, based on a single radio frequency current pulse input at the input port of the RSFQ pulse multiplier, in order to generate a larger voltage across the converter.

[0010] In one embodiment, the quantum mechanical system further includes an m-stage fast single-throughput quantum (RSFQ) pulse multiplier connected in series. The m-stage RSFQ pulse multiplier is configured to generate an RF current (I), which is given by the following formula: I = 2 m xΦ0x f clk / R, where Φ0 is the superconducting magnetic flux quantum, f clk R is the RF frequency of the RF current, and R is the resistance value of the resistor.

[0011] In one embodiment, the quantum mechanical system includes a plurality of radio frequency (RF) to direct current (DC) converters; and a plurality of quantum mechanical devices, each of which is connected to a corresponding RF to DC converter among the plurality of RF to DC converters. The plurality of RF to DC converters are addressable such that the SFQ pulse generated according to the RF current is routed to the desired converter among the plurality of RF to DC converters.

[0012] In one embodiment, the quantum mechanical system further includes: an input port configured to receive the direct current (DC) and the radio frequency (RF) current; and a plurality of address lines, each address line having at least one demultiplexer (DEMUX), with the demultiplexer (DEMUX) in a first address line connected to the input port. Each of the plurality of radio frequency (RF) to direct current (DC) converters is connected to a corresponding demultiplexer (DEMUX) in the at least one demultiplexer (DEMUX).

[0013] In one embodiment, the demultiplexer (DEMUX) in the first address line is connected to two demultiplexers (DEMUX) in the second address line, and each of the two demultiplexers is connected to at least two radio frequency (RF) to direct current (DC) converters.

[0014] Another aspect of the present invention provides a bipolar quantization supercurrent generator (QSG) comprising: a first input port configured to receive at least one incremental single-flux quantum pulse; and a second input port configured to receive at least one decrementing single-flux quantum pulse. The QSG further comprises: a first Josephson junction (JJ) connected to the first input port and a second Josephson junction (JJ) connected to the second input port, the first and second Josephson junctions being further grounded; and an inductor (Lq) connected to the first and second Josephson junctions. The inductor (Lq), the first and second Josephson junctions (JJs) form a superconducting quantum interference device (SQUID) loop. In operation, the current circulating in the storage SQUID loop formed by the first and second Josephson junctions and the inductor (Lq) increases or decreases by an increment based on at least one incremental single-flux quantum pulse input through the first input port or at least one decrementing single-flux quantum pulse input through the second input port.

[0015] In an embodiment, the current circulating in the storage SQUID loop increases or decreases by a current increment ΔI given by the following equation: ΔI = Φ0 / Lq, where Φ0 is the superconducting magnetic flux quantum and Lq is the inductance value (Lq) of the inductor.

[0016] In an embodiment, the QSG further includes a third input port connected to the first Josephson junction (JJ), the second Josephson junction (JJ), and the inductor (Lq). The third input port is configured to input a bias DC current into the storage loop to electrically bias the first Josephson junction and the second Josephson junction such that the first Josephson junction and the second Josephson junction generate pulses when pulses are applied to their respective inputs.

[0017] In an embodiment, the screening parameter βL of the SQUID loop depends on the critical current I of the first Josephson junction and the second Josephson junction in the SQUID loop, as well as the inductance value of the inductor connecting the first Josephson junction and the second Josephson junction.

[0018] In an embodiment, the QSG further includes a third Josephson junction (JJ) and a fourth Josephson junction (JJ). The third Josephson junction is connected to the first Josephson junction (JJ) and the first input port via a first sensing line, and the fourth Josephson junction is connected to the second Josephson junction (JJ) and the second input port via a second sensing line. The first Josephson junction (JJ) and the third Josephson junction (JJ) form a first Josephson transmission line (JTL), and the second Josephson junction (JJ) and the fourth Josephson junction (JJ) form a second Josephson transmission line (JTL).

[0019] Another aspect of the present invention is to provide a quantum mechanical system including the aforementioned QSG. In one embodiment, the quantum mechanical system further includes a plurality of bipolar quantized supercurrent generators (QSGs); and a plurality of quantum mechanical devices, each of the plurality of quantum mechanical devices being inductively coupled to a corresponding QSG among the plurality of QSGs. The plurality of QSGs are addressable such that an input SFQ pulse is routed to a desired QSG among the plurality of QSGs.

[0020] In one embodiment, the quantum mechanical system further includes an input port configured to receive direct current (DC) and single-through-quantum (SFQ) radio frequency current; and a plurality of address lines, each address line having at least one demultiplexer (DEMUX), with the demultiplexer (DEMUX) in the first address line connected to the input port. Each QSG is connected to a corresponding demultiplexer (DEMUX) in at least one demultiplexer (DEMUX). Attached Figure Description

[0021] The operation and function of the relevant elements of this disclosure and structure, as well as the economy of combination and manufacture of the components, will become more apparent when the following description and appended claims are considered in conjunction with the accompanying drawings, all of which form part of this specification, wherein similar reference numerals denote corresponding components in the various drawings. However, it should be clearly understood that the drawings are for illustrative and descriptive purposes only and are not intended to be limiting of the invention.

[0022] Figure 1 This is a schematic electronic circuit of a radio frequency (RF) to direct current (DC) converter according to an embodiment of the present invention;

[0023] Figure 2The results are current-voltage graphs of simulations (e.g., using WRSpice) of 20JJ (e.g., fed Josephson transmission line - FJTL) for different drive frequencies (the frequencies shown are 5 GHz, 7 GHz, 9 GHz, 11 GHz, 13 GHz, and 15 GHz) according to embodiments of the present invention.

[0024] Figure 3 This is a graph showing the relationship between the output resistor current (in A) as a function of the RF drive frequency according to an embodiment of the present invention and the time (in ns) obtained from a dynamic simulation (e.g., using WRSpice) of the current through a series combination of a 130pH inductor and a 0.1 resistor driven from a 20JJ F JTL.

[0025] Figure 4 It includes embodiments of the present invention. Figure 1 The block diagram shown is of the quantum mechanical system of the RF-DC converter.

[0026] Figure 5 is a schematic electronic circuit of an exemplary conventional fast single-throughput quantum (RSFQ) pulse frequency multiplier;

[0027] Figure 6 This is a diagram of a single pulse input to a series array of five cascaded RSFQ pulse multipliers according to an embodiment of the present invention, and multiple pulses output by the RSFQ pulse multipliers;

[0028] Figure 7 This is a schematic diagram illustrating how a single DC / SFQ converter 106, according to an embodiment of the present invention, can provide a controllable fast throughput bias to multiple devices (DUTs) via multiple RF-to-DC converters;

[0029] Figure 8 This is a schematic electronic circuit of a bipolar quantization overcurrent generator (QSG) according to an embodiment of the present invention;

[0030] Figures 9A to 9D An embodiment according to the present invention is shown. Figure 8 Dynamic simulation of the dual-polarization overcurrent generator (QSG) shown; and

[0031] Figure 10 This is a schematic diagram of a quantum mechanical system using the QSG shown in the figure according to an embodiment of the present invention. Specific Implementation

[0032] Figure 1This is an illustrative electronic circuit of a radio frequency (RF) to direct current (DC) converter according to an embodiment of the present invention. The RF to DC converter 100 includes a direct current (DC) input port 102 and an RF input port 104. The converter 100 also includes a 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 into SFQ current pulses. The RF to DC converter 100 also includes a Josephson junction (JJ) 108A, which is connected to 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 is grounded 116. The converter 100 also includes a resistor 118, which is connected to the Josephson junction (JJ) 108A via a third induction line 120 and is connected to the DC input port 102.

[0033] In operation, when a DC current is applied via the DC input port 102, the DC current is shunt to ground 116 through JJ108A, and essentially no DC current flows through resistor 118. When an RF current is applied via the RF input port 104, the output sequence of SFQ current pulses from the DC-to-SFQ converter 106, having a pulse-to-pulse interval inversely proportional to the frequency of the RF current, causes the Josephson junction (JJ) 108A to switch at a rate commensurate with the RF frequency of the RF current, so as to linearly generate a steady-state voltage across the Josephson junction (JJ) 108A depending on the RF frequency, such that the current flowing through resistor 118 is directly dependent on the RF frequency of the RF current.

[0034] In an embodiment, the converter 100 further includes a plurality of Josephson junctions 108A, 108B, 108C, 108D, which are connected to the DC input port 102 via a first sensing line 110 and to the RF input port 104 via a second sensing line 112 via a DC-to-SFQ converter 106 and grounded 116. Although Figure 1 Four Josephson junctions are depicted, but it is understood that any number of Josephson junctions can be used, such as two, three, or more. Multiple Josephson junctions 108A, 108B, 108C, and 108D are configured to switch at a rate commensurate with the RF frequency of an RF current when an RF current is applied via RF input port 104, to linearly generate a steady-state voltage across the multiple Josephson junctions (JJs) 108A, 108B, 108C, and 108D depending on the RF frequency, such that the current flowing through resistor 118 is directly dependent on the RF frequency of the RF current. It may be noteworthy that the more JJs used in an FJTL, the greater the amount of RF-driven current the FJTL can obtain.

[0035] like Figure 1 As shown, when a global bias current is applied at DC input port 102, the current is entirely diverted to ground through JJ 108A, 108B, 108C, and 108D (upward arrow), and no current (downward arrow) flows through the resistor path (i.e., resistor 118) toward the device under test (DUT) (not shown). When an RF current is applied at RF input port 104, JJ 108A, 108B, 108C, and 108D begin to switch at a rate commensurate with the frequency of the applied RF tone and linearly form a steady-state voltage depending on the drive frequency. The FJTL generates a steady-state DC voltage (V) across the Josephson junctions (JJs) 108A, 108B, 108C, and 108D, which is expressed according to the following equation with respect to the RF frequency (f). clk Proportional:

[0036] V=Φ0x f clk

[0037] Where Φ0 is the superconducting magnetic flux quantum.

[0038] Then, this voltage drives current through resistor 118, where the magnitude of the current is determined by Ohm's law I = V / R = Φ0x f clk / R is given. Thus, the final relationship shows that the circuit is a true RF frequency to DC current converter, where linear scaling is set by the flux quantum and the shunt resistor.

[0039] Figure 2 This is a current-voltage graph showing the results of simulations (e.g., using WRSpice) of 20 JJs (e.g., fed Josephson transmission lines - FJTLs) at different drive frequencies (shown as 5 GHz, 7 GHz, 9 GHz, 11 GHz, 13 GHz, and 15 GHz) according to embodiments of the present invention. In this embodiment, all JJs have a critical current of 250 A, resulting in a total critical current of 5 mA for the circuit. Figure 2 The diagram shows that for all applied frequencies, the Shapiro step begins at approximately 1.5 mA of the DC bias applied to the FJTL. For example, when globally biased at approximately 3.5 mA, the FJTL can supply or sink up to approximately 1.5 mA of current and remain operational. The resulting voltage across the FJTL is extremely stable over a wide range of global bias currents.

[0040] Figure 3This is a graph showing the relationship between the output resistor current (in A) as a function of the RF drive frequency and the time (in ns) obtained from a dynamic simulation (e.g., using WRSpice) of the current driven from a 20JJ FJTL through a series combination of a 130pH inductor and a 0.1Ω resistor, according to an embodiment of the present invention. WRSpice is a circuit simulation and analysis tool manufactured by Whiteley Research. At time t = 0 ns, a 5 GHz RF current is applied to the DC / SFQ converter 106. The output pulse from the converter 106 is then fed into an FJTL with a 20JJ. The FJTL forms a voltage (approximately 10 μV at 5 GHz), which then drives a 100A current through resistor 118 at a characteristic time t = L / R = 1.3 ns. At time t = 50 ns, the RF drive frequency input through RF input port 104 is changed to 10 GHz, and the resulting current driven through resistor 118 is doubled. Finally, at time t = 100 ns, the RF drive frequency was reset to 5 GHz, causing the current through resistor 118 to return to its original value of 100 μA.

[0041] Figure 4 This is a block diagram of a quantum mechanical system 200 including an RF-to-DC converter 100 according to an embodiment of the present invention. The quantum mechanical system 200 includes the RF-to-DC converter 100, which may be equipped with, for example, one or more Josephson junctions JJ 108A, 108B, 108C, 108D. In one embodiment, the quantum mechanical system 200 further includes at least one quantum mechanical device 202 connected to a resistor 118 of the RF-to-DC converter 100. In one embodiment, the one or more devices 202 include at least one of a qubit, a superconducting quantum interference device, or a non-quantum mechanical circuit (e.g., like a transistor or other circuit).

[0042] In embodiments, it may be advantageous to increase the operating voltage of the FJTL. To increase the operating voltage, the quantum mechanical system 200 may include one or more fast single-throughput quantum (RSFQ) pulse multiplier stages 204. One or more RSFQ pulse multiplier stages 204 may be provided before the RF-to-DC converter 100 to achieve a 2:1 increase in operating voltage. m The increased gain, where m is the number of RSFQ pulse multiplier stages.

[0043] Figure 5 is a schematic electronic circuit of an exemplary conventional fast single-throughput quantum (RSFQ) pulse multiplier 204. The RSFQ pulse multiplier 204 has an input port 502 and an output port 504. The output port 504 of the RSFQ pulse multiplier 204 is connected to the input port 104 of a DC-to-SFQ converter 100. The RSFQ pulse multiplier 204 is configured to generate a single-throughput quantum (SFQ) pulse current input through the input port 104 of the DC-to-SFQ converter 100. However, other types of RSFQ pulse multipliers can also be used.

[0044] Figure 6 This is a diagram illustrating a single pulse input to the RSFQ pulse multiplier 204 and multiple pulses output by the RSFQ pulse multiplier 204 according to an embodiment of the present invention. In this embodiment, the RSFQ pulse multiplier 204 is configured to generate multiple current pulses 604 at twice the SFQ pulse rate applied at the output port of the RSFQ pulse multiplier 204 based on a single RF current pulse 602 input at the input port of the RSFQ pulse multiplier 204, in order to generate a larger voltage across the converter 100. In this embodiment, an m-level fast single-throughput quantum (RSFQ) pulse multiplier 204 connected in series can be used. For example, Figure 6 The simulation results (e.g., using WRSpice) of five cascaded RSFQ pulse multipliers 204 shown in Figure 5 are illustrated. The m-stage of the RSFQ pulse multiplier 204 can be configured to generate an RF current (I), which is given by the following formula:

[0045] I = 2 m xΦ0x f clk / R

[0046] Where Φ0 is the superconducting magnetic flux quantum, f clk R is the RF frequency of the RF current, and R is the resistance value of the resistor.

[0047] In this embodiment, when the input pulse arrives at input port 502, Josephson junctions J1 and J2 switch sequentially. The SFQ pulse from J2 splits between the upper path formed by Josephson junctions J4 and J5 and the lower branch formed by Josephson junctions J2 and J3. The shunt resistor Rs in the lower branch sets the L / R rise time of the current in the lower branch, thereby delaying any switching action in Josephson junction J3. The upper branch pulse switches Josephson junction J5, which delivers the pulse to output port 504 while also driving current into Josephson junctions J3 and J4. This additional current, along with the current from the delayed switching current from Josephson junction J2, forces Josephson junction J3 to switch and generates a second pulse at the output. Josephson junction J4 acts as a protective junction to prevent Josephson junction J2 from switching twice. For m stages placed in series, the resulting current driven by the RF-to-DC converter 100 is I = 2. m xΦ0x f clk / R. The circuit and its operation are derived from pre-existing literature. Does that matter?

[0048] Figure 7 This is a schematic diagram illustrating how a single DC / SFQ converter 106, according to an embodiment of the invention, can provide a controllable fast throughput bias to multiple devices (DUTs) via multiple RF-to-DC converters. In this embodiment, the quantum mechanical system 200 includes multiple radio frequency (RF) to direct current (DC) converters 100. The quantum mechanical system 200 also includes multiple device DUTs (e.g., quantum mechanical devices) 202. Each of the multiple quantum mechanical devices 202 is connected to a corresponding RF-to-DC converter among the multiple RF-to-DC converters 100. The multiple RF-to-DC converters 100 are addressable such that an SFQ pulse generated by the DC / SFQ converter 106 based on an RF current is routed to the desired converter among the multiple RF-to-DC converters (FJTLs) 100.

[0049] In one embodiment, the quantum mechanical system 200 further includes: an input port 702 configured to receive direct current (DC) and radio frequency (RF) current; and a plurality of address lines 704, each address line 704 having at least one demultiplexer (DEMUX) 706. The demultiplexer (DEMUX) 706A in the first address line 704A is connected to the input port 702 via a DC / SFQ converter 106. Each of the plurality of radio frequency (RF) to direct current (DC) converters (FJTLs) 100 is connected to a corresponding demultiplexer (DEMUX) in at least one demultiplexer (DEMUX) 706.

[0050] In an embodiment, a demultiplexer (DEMUX) 706A in the first address line 704A is connected to two demultiplexers (DEMUX) 706 in the second address line 704B, and each of the two demultiplexers 706 is connected to at least two radio frequency (RF) to direct current (DC) converters (FIJTL) 100.

[0051] Therefore, in this embodiment, a series combination of a multi-stage RSFQ pulse multiplier 204 and a resistor-shunt FJTL 100 can be placed at the end of the RSFQ DEMUX tree so that a single DC / SFQ converter source 106 can drive multiple devices (DUTs) 202. Figure 7 As shown, a single DC / SFQ converter 106 drives the input of the flux bias 1:2DEMUX 706. Depending on the sign of the current in the corresponding address line 704, the flux pulse from the DC / SFQ converter 106 is routed to the left or right of the 1:2DEMUX 704.

[0052] Figure 8 This is a schematic electronic circuit of a bipolar quantization supercurrent generator (QSG) 800 according to an embodiment of the present invention. The bipolar quantization supercurrent generator (QSG) 800 includes: a first input port 802 configured to receive at least one incremental single-throughput quantum pulse and a second input port 804 configured to receive at least one decremental single-throughput quantum pulse. The QSG 800 also includes: a first Josephson junction (JJ) 806 connected to the first input port 802 and a second Josephson junction (JJ) 808 connected to the second input port 804. The first Josephson junction 806 and the second Josephson junction 808 are further grounded at 809. The QSG 800 also includes an inductor (Lq) 810 connected to the first Josephson junction 806 and the second Josephson junction 808. The inductor (Lq) 810, the first Josephson junction (JJ) 806, and the second Josephson junction (JJ) 808 form a superconducting quantum interference device (SQUID) loop. In operation, the current circulating in the storage SQUID loop formed by the first Josephson junction 806, the second Josephson junction 808, and the inductor (Lq) 810 is increased or decreased by increments based on at least one incremental single-through quantum pulse input through the first input port 802 or at least one decremental single-through quantum pulse input through the second input port 804.

[0053] In an embodiment, the current circulating in the storage SQUID loop increases or decreases by the current increment ΔI given by the following equation:

[0054] ΔI=Φ0 / Lq

[0055] Where Φ0 is the superconducting magnetic flux quantum and Lq is the inductance value of the inductor (Lq).

[0056] In an embodiment, the QSG 800 further includes a third input port 813 connected to a first Josephson junction (JJ) 806, a second Josephson junction (JJ) 808, and an inductor (Lq) 810. The third input port 813 is configured to input a bias DC current to the storage loop input so that the first Josephson junction 806 and the second Josephson junction 808 are electrically biased such that the first Josephson junction 806 and the second Josephson junction 808 generate pulses when pulses are applied to their respective inputs.

[0057] In the embodiment, the filtering parameter β of the SQUID loop L It depends on the critical current I of the first Josephson junction 806 and the second Josephson junction 808 in the SQUID loop and the inductance value of the inductor connecting the first Josephson junction and the second Josephson junction.

[0058] In an embodiment, QSG 800 further includes a third Josephson junction (JJ) 812, which is connected to the first Josephson junction (JJ) 806 and the first input port 802 via a first sensing line 816. QSG 800 also includes a fourth Josephson junction (JJ) 814, which is connected to the second Josephson junction (JJ) 808 and the second input port 804 via a second sensing line 818. The first Josephson junction (JJ) 806 and the third Josephson junction (JJ) 812 form a first Josephson transmission line (JTL) 819, and the second Josephson junction (JJ) 808 and the fourth Josephson junction (JJ) 814 form a second Josephson transmission line (JTL) 820.

[0059] In this embodiment, when the SFQ pulse arrives at the first input port "Inc" 802, it triggers the switching of nodes J1 812 and J2 806, establishing a circulating current (arrow from left to right) flowing from J2 812 through Lq 810. The user can reset this circulating current by triggering junctions J3 808 and J4 814 from the second input port "Dec" 804 to circulate the current flowing from J3 808 through Lq 810 (arrow from right to left). Because the sensed value Lq (and therefore β1) is so large, the circulating current is not large enough to over-bias or under-bias nodes J3 808 or J2 806, thus allowing multiple pulses to be applied continuously from the first input port "Inc" 802 or the second input port "Dec" 804. The SFQ pulse loaded from the first input port 802 or the second input port 804 will increase or decrease the current in the storage loop formed by Lq and junctions J2 806 and J3 808 by an increment ΔI = Φ0 / Lq. In the embodiment, β LIt equals approximately 100.

[0060] Therefore, the storage inductor Lq, together with the first Josephson transmission line (JTL) 819 and the last stage JJ (in this case J2806 and J3808) of the second Josephson transmission line (JTL) 820, respectively form a β having, for example, equal to approximately 100. L A superconducting quantum interference device (SQUID) is used. This allows the storage of multiple flux quanta that can be loaded from a JTL (first JTL 819 or second JTL 820), resulting in the current in Lq being incremented or decremented precisely in steps ΔI = Φ0 / Lq. Once the appropriate amount of current has been loaded into Lq as determined by the user, the circuit can be de-energized, where the flux is permanently stored in the loop. In an embodiment, the QSG 800 may support cyclic current flux quantum values ​​of 100-1000 depending on the value of Lq, thus allowing for flux bias in precise steps of approximately 0.01-0.001Φ0.

[0061] Figures 9A to 9D An embodiment according to the present invention is shown. Figure 8 The dynamic simulation of the dual-polarization overcurrent generator (QSG) 800 is shown. Figure 9B As shown, when loading from the second input port "Dec" 804 Figure 9A During the pulse shown, the current I(Lq) in Lq decreases by a quantization amount Φ0 / Lq. For example... Figure 9D As shown, when Figure 9C When the pulse shown is applied to the first input port "Inc" 802, the current is increased by the same quantization amount per flux pulse (increasing the number of stages from left to right). An SFQ pulse applied to the first input port "Inc" 802 increases the current stored in the loop by the same quantization amount. A transition from one stage to the next occurs when the pulse is applied. (As shown...) Figure 9D As shown, the SFQ pulse applied to the second input port 804 reduces the current stored in the quantization inductor Lq by a quantization level (decreasing from left to right).

[0062] Figure 10 This is a use according to an embodiment of the present invention. Figure 8A schematic diagram of a quantum mechanical system 1000 with QSG 800 shown. The quantum mechanical system 1000 includes a bipolar quantized supercurrent generator (QSG) 800. In an embodiment, the quantum mechanical system includes a plurality of QSGs 800. In another embodiment, the quantum mechanical system also includes a plurality of quantum mechanical devices 1002. Each of the plurality of quantum mechanical devices 1002 is inductively coupled to a corresponding QSG 800 among the plurality of QSGs 800, for example, via an inductor 1004. The plurality of QSGs 800 are addressable such that an input SFQ pulse from a DC / SFQ converter 1006 is routed to a desired QSG among the plurality of QSGs 800.

[0063] In one embodiment, the quantum mechanical system 1000 further includes an input port 1008 configured to receive direct current (DC) and single-throughput quantum (SFQ) radio frequency current. The quantum mechanical system 1000 also includes a plurality of address lines 1010. Each address line 1010 has at least one demultiplexer (DEMUX) 1012. The demultiplexer (DEMUX) 1012A in the first address line 1010A is connected to the input port 1008. Each QSG 800 is connected to a corresponding demultiplexer (DEMUX) in at least one demultiplexer (DEMUX) 1012.

[0064] In this embodiment, a single DC / SFQ converter 1006 can provide bipolar flux bias to multiple different qubits 1002. The polarity of the current on address line 1010 determines whether the SFQ pulse from the DC / SFQ converter 1006 is routed to the left or right output of the 1:2 DEMUX 1012. In a final stage, the polarity of the current on the address line determines whether the pulse is sent to the first input port "Inc" 802 or the second input port "Dec" 804 of the corresponding QSG 800. This can provide positive and negative flux bias when the QSG 800 is coupled to the SQUID loop of the superconducting qubit (QB) 1002. The scaling of the number of devices (e.g., qubits) that can be biased in this configuration with the number of address lines is 2. (n-1) , where n is the number of address lines.

[0065] One advantage of using the QSG 800 of this invention is the ability to generate a bipolar continuous current with zero quiescent power dissipation. This opens the door to efficiently passing the bias circuit within the cryostat at any temperature stage. Furthermore, when combined with the additional benefits of the DEMUXING control signal, the QSG... Figure 10 Together, the DEMUX configuration shown provides a scalable path to a DC flux-biased quantum processor with 1000 devices (e.g., qubits), where the number of control lines used decreases exponentially from room temperature.

[0066] Various embodiments of the invention have been described for illustrative purposes, but are not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein has been chosen to best explain the principles of the embodiments, their practical application, or technical improvements to technologies found in the market, or to enable those skilled in the art to understand the embodiments disclosed herein.

Claims

1. A radio frequency (RF) to DC converter, comprising: DC input port; RF input port; A DC-to-SFQ converter is connected to the RF input port, and the DC-to-SFQ converter is configured to convert RF current into SFQ current pulses; Josephson junction JJ, which is connected to the DC input port via a first inductive line and to the DC-to-SFQ converter via a second inductive line, and is grounded; and A resistor, which is connected to the Josephson junction via a third inductive line and is connected to the DC input port, wherein, in operation, when a DC current is applied via the DC input port, no DC current flows through the resistor, and when an RF current of the RF frequency is applied via the RF input port, the current flowing through the resistor is directly dependent on the RF frequency based on the SFQ current pulse from the DC-to-SFQ converter that switches the JJ; A fast single-throughput quantum RSFQ pulse multiplier with an input port and an output port, wherein the output port of the RSFQ pulse multiplier is connected to the input port of the DC-to-SFQ converter, and the RSFQ pulse multiplier is configured to generate an SFQ pulse current input through the input port of the DC-to-SFQ converter.

2. The converter according to claim 1, wherein, When the RF current is applied via the RF input port, the output sequence of SFQ current pulses from the DC-SFQ converter, having a pulse-to-pulse interval inversely proportional to the frequency of the RF current, causes the Josephson junction JJ to switch at a rate commensurate with the RF frequency of the RF current, so as to linearly generate a steady-state voltage across the Josephson junction JJ depending on the RF frequency.

3. The converter according to any one of claims 1-2, further comprising: Multiple Josephson junctions are connected to the DC input port via the first sensing line and to the RF input port via the DC-to-SFQ converter via the second sensing line, and are grounded. The plurality of Josephson junctions are configured to switch at a rate commensurate with the RF frequency of the RF current when the RF current is applied via the RF input port, so as to linearly generate a steady-state voltage across the plurality of Josephson junctions JJ depending on the RF frequency, such that the current flowing through the resistor is directly dependent on the RF frequency of the RF current.

4. The converter according to claim 2, wherein, According to the following equation, the steady-state voltage V across the Josephson junction JJ is related to the RF frequency f. clk Proportional: V = Φ0 f clk Where Φ0 is the superconducting magnetic flux quantum.

5. A quantum mechanical system, comprising: RF to DC converters, including: DC input port; RF input port; A DC-to-SFQ converter is connected to the RF input port, and the DC-to-SFQ converter is configured to convert RF current into SFQ current pulses; Josephson junction JJ, which is connected to the DC input port via a first inductive line and to the DC-to-SFQ converter via a second inductive line, and is grounded; and A resistor, connected to the Josephson junction and the DC input port via a third inductive line, wherein, in operation, when a DC current is applied via the DC input port, the DC current is shunt to ground through the Josephson junction JJ and substantially no current flows through the resistor, and when an RF current is applied via the RF input port, the Josephson junction JJ switches at a rate commensurate with the RF frequency of the RF current to linearly generate a steady-state voltage across the Josephson junction JJ depending on the RF frequency, such that the current flowing through the resistor is directly dependent on the RF frequency of the RF current; A fast single-throughput quantum RSFQ pulse multiplier with an input port and an output port, wherein the output port of the RSFQ pulse multiplier is connected to the input port of the DC-to-SFQ converter, and the RSFQ pulse multiplier is configured to generate an SFQ pulse current input through the input port of the DC-to-SFQ converter.

6. The quantum mechanical system according to claim 5, further comprising: At least one quantum mechanical device connected to the resistor.

7. The quantum mechanical system according to claim 6, wherein, The at least one quantum mechanical device includes at least one of a qubit, a superconducting quantum interference device, a transistor, or other circuit.

8. The quantum mechanical system according to claim 5, wherein, The RSFQ pulse multiplier is configured to generate multiple current pulses at twice the rate of an SFQ pulse applied at the output port of the RSFQ pulse multiplier, based on a single RF current pulse input at the input port of the RSFQ pulse multiplier, in order to generate a larger voltage across the converter.

9. The quantum mechanical system according to claim 8, further comprising: A series-connected m-level fast single-throughput quantum RSFQ pulse frequency multiplier The m-stage RSFQ pulse multiplier is configured to generate an RF current I, which is given by the following formula: I = 2 m Φ0 f clk / R Where Φ0 is the superconducting magnetic flux quantum, f clk R is the RF frequency of the RF current, and R is the resistance value of the resistor.

10. The quantum mechanical system according to any one of claims 5 to 9, further comprising: Multiple RF to DC converters; as well as Multiple quantum mechanical devices, each of which is connected to a corresponding RF-to-DC converter among the multiple RF-to-DC converters. The plurality of RF-to-DC converters are addressable such that the SFQ pulse generated based on the RF current is routed to the desired converter among the plurality of RF-to-DC converters.

11. The quantum mechanical system of claim 10, further comprising: An input port is configured to receive the DC current and the RF current; as well as Multiple address lines, each address line having at least one demultiplexer (DEMUX), and the demultiplexer (DEMUX) in the first address line is connected to the input port. Each of the plurality of RF-to-DC converters is connected to a corresponding demultiplexer DEMUX in the at least one demultiplexer DEMUX.

12. The quantum mechanical system according to claim 11, wherein, The demultiplexer DEMUX in the first address line is connected to two demultiplexers DEMUX in the second address line, and each of the two demultiplexers is connected to at least two RF to DC converters.

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