Radio Frequency (RF) to Direct Current (DC) Converter and Bipolar Quantized Superconducting Current Generator (QSG)

Abstract

A radio frequency (RF) to direct current (DC) converter is provided in which, when a DC current is applied through a DC input port of the converter, the DC current is shunted to ground through Josephson junctions (JJs) of the converter, with substantially no DC current flowing through resistors of the converter, and when an RF current is applied through an RF input port of the converter, an output train of SFQ current pulses from the DC-SFQ converter of the RF-DC converter, having an inter-pulse spacing that is inversely proportional to the RF current frequency, causes the JJs to switch at a rate equivalent to the RF frequency of the RF current to produce a steady-state voltage across the JJ that is linearly dependent on the RF frequency.

Description

[Technical Field]

[0001] Presently claimed embodiments of the present invention relate to quantum computing, and more particularly to radio frequency (RF) to direct current (DC) converters and bipolar quantized superconducting current generators (QSGs) and quantum mechanical systems employing them. [Background technology]

[0002] The application of fast magnetic flux bias pulses has traditionally been achieved with room-temperature gigasamples-per-second (GS / s) digital-to-analog converters (DACs) that drive current into a temperature T=4K resistor, with pulse amplitude accuracy set by the number of DAC bits and the Johnson noise of the bias resistor. However, this method suffers from significant pulse shape distortion because the current pulse must pass through multiple temperature stages and filtering before reaching the intended device (device under test—DUT). In addition, voltage DACs with relatively large counts are required to achieve accurate pulse heights. Furthermore, the wiring required to bias multiple n devices scales linearly with the number n of devices. Therefore, it is desirable to provide a new method or system for generating fast current pulses that can either be applied directly to the device (DUT) or coupled as magnetic flux through a pair of mutual inductors.

[0003] Additionally, application of static flux bias to superconducting circuits has primarily been accomplished via application of a voltage to a cold resistor (e.g., at a temperature T of approximately 4 K), which then drives a current through a primary inductance loop interconnected to the device under test (DUT). Scaling of this approach in terms of room-temperature wiring and voltage supply overhead is linear in the number of devices under test (DUT) for which flux biasing is desired. The thermal load and physical space required to accommodate the hundreds, if not thousands, of physical devices (e.g., qubits) required to demonstrate quantum advantage through the implementation of computing paradigms such as surface codes are untenable. Therefore, it would also be desirable to provide a new method or system for generating bipolar flux bias currents, thereby improving the scaling of the number of devices to room-temperature control lines 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 provides a radio frequency (RF) to direct current (DC) converter including a direct current (DC) input port, a radio frequency (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 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 wire and to the DC to SFQ converter via a second inductive wire and connected to ground, and a resistor connected to the Josephson junction and to the DC input port via a third inductive wire. In operation, when a DC current is applied through the DC input port, the DC current is shunted to ground through the JJ and substantially no DC current flows through the resistor; when an RF current is applied through the RF input port, an output train of SFQ current pulses from the DC-SFQ converter having an inter-pulse spacing that is inversely proportional to the RF current frequency causes the Josephson junctions (JJs) to switch at a rate equal to the RF frequency of the RF current, thereby generating a steady-state voltage across the Josephson junctions (JJs) that is linearly dependent on the RF frequency, and as a result, the current flowing through the resistor depends directly on the RF frequency of the RF current.

[0005] In an embodiment, the converter further includes a plurality of Josephson junctions connected to the DC input port via a first inductive wire and to the RF input port via a DC-SFQ converter via a second inductive wire and connected to ground, the plurality of Josephson junctions configured, when an RF current is applied via the RF input port, to switch at a rate comparable to an RF frequency of the RF current to produce a steady-state voltage across the plurality of Josephson junctions (JJs) that is linearly dependent 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 a Josephson junction (JJ) is calculated using the following equation: V=Φ×f clk According to the RF frequency (f clk), where Φ is the superconducting magnetic flux quantum.

[0007] A further aspect of the present invention provides a quantum mechanical system including the radio frequency (RF) to direct current (DC) converter described above. In embodiments, the quantum mechanical system further includes at least one quantum mechanical device connected to the resistor. In embodiments, the one or more devices include, for example, a qubit, a superconducting quantum interference device, or a non-quantum mechanical device.

[0008] In an embodiment, the quantum mechanical system further includes a rapid single flux quantum (RSFQ) pulse doubler having an input port and an output port, the output port of the RSFQ pulse doubler being connected to the input port of the DC-SFQ converter, and the RSFQ pulse doubler being configured to generate an SFQ pulse current input through the input port of the DC-SFQ converter.

[0009] In an embodiment, the RSFQ pulse doubler is configured to generate multiple current pulses from a single radio frequency current pulse input at the input port of the RSFQ pulse doubler at twice the rate of the applied SFQ pulse at the output port of the RSFQ pulse doubler, thereby generating a larger voltage across the converter.

[0010] In an embodiment, the quantum mechanical system further includes m stages of a serially connected rapid single flux quantum (RSFQ) pulse doubler, where the m stages of the RSFQ pulse doubler are represented by the following equation: I=2 m ×Φ0×f clk is configured to generate an RF current (I) given by / R, where Φ is the superconducting magnetic flux quantum and f clk is the RF frequency of the RF current, and R is the resistance of the resistor.

[0011] In an 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 one of the plurality of RF-DC converters, and the plurality of RF-DC converters are addressable so that the SFQ pulses generated from the RF current are routed to a desired converter among the plurality of RF-DC converters.

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

[0013] In an embodiment, a demultiplexer (DEMUX) on a first address line is connected to two demultiplexers (DEMUX) on a 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 quantized superconducting current generator (QSG) including 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 decremental single flux quantum pulse. The QSG further includes a first Josephson junction (JJ) connected to the first input port and a second Josephson junction (JJ) connected to the second input port, wherein the first and second Josephson junctions are further connected to ground, and an inductor (L) connected to the first and second Josephson junctions. q ) and the inductor (L q) and the first and second Josephson junctions (JJs) form a superconducting quantum interference device (SQUID) loop. During operation, the first and second Josephson junctions and the inductor (L q ) and the current circulating in the storage SQUID loop formed by the first input port gradually increases or decreases based on at least one increment single flux quantum pulse input through the first input port or at least one decrement single flux quantum pulse input through the second input port, respectively.

[0015] In an embodiment, the current circulating in the storage SQUID loop is given by the following equation: ΔI=Φ / L q It is increased or decreased by a current increment ΔI given by, where Φ is the superconducting flux quantum and L q is the inductor (L q ) is the inductance value.

[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 configured to input a bias direct current (DC) into the storage loop to electrically bias the first and second Josephson junctions, such that the first and second Josephson junctions generate a pulse when a pulse is applied to their respective inputs.

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

[0018] In an embodiment, the QSG further includes a third Josephson junction (JJ) connected to the first Josephson junction (JJ) and the first input port via a first inductive line, and a fourth Josephson junction (JJ) connected to the second Josephson junction (JJ) and the second input port via a second inductive line, wherein 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 provides a quantum mechanical system including the above-described QSG. In an embodiment, the quantum mechanical system further includes a plurality of bipolar quantum superconducting current generators (QSGs) and a plurality of quantum mechanical devices, each of which is inductively coupled to a corresponding one of the plurality of QSGs. The plurality of QSGs are addressable so that an input SFQ pulse is routed to a desired QSG among the plurality of QSGs.

[0020] In an embodiment, the quantum mechanical system further includes an input port configured to receive direct current (DC) and single flux quantum (SFQ) radio frequency currents, and a plurality of address lines, each address line having at least one demultiplexer (DEMUX), the demultiplexer (DEMUX) in a first address line being connected to the input port, and each QSG being connected to a corresponding one of the at least one demultiplexer (DEMUX). [Brief explanation of the drawings]

[0021] The present disclosure, as well as the method of operation and function of the associated elements of construction and combination of parts and economy of manufacture, will become more apparent from a consideration of the following description and appended claims, with reference to the accompanying drawings, all of which form a part of this specification, and in which like reference characters designate corresponding parts in the various drawings. 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.

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

[0023] [Figure 2] 1 is a current-voltage plot resulting from a simulation (e.g., using WRSpice) of 20 JJs (e.g., fed Josephson transmission lines - FJTLs) 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.

[0024] [Figure 3] FIG. 10 is a plot of output resistor current (in μA) versus time (in ns) obtained from a dynamic simulation (e.g., using WRSpice) of current driven through a series combination of a 130 pH inductor and a 0.1 resistor from 20 JJ FJTLs as a function of RF drive frequency, according to an embodiment of the invention.

[0025] [Figure 4] 2 is a block diagram of a quantum mechanical system including the RF-DC converter shown in FIG. 1 according to an embodiment of the present invention.

[0026] [Figure 5] 1 is a schematic electronic circuit diagram of an exemplary conventional rapid single flux quantum (RSFQ) pulse doubler.

[0027] [Figure 6] 1 is a plot of a single pulse input to a serial array of five cascaded RSFQ pulse doublers and multiple pulses output by the RSFQ pulse doublers, according to an embodiment of the present invention.

[0028] [Figure 7] FIG. 1 is a schematic diagram illustrating how a single DC / SFQ converter 106 can controllably provide fast flux bias to multiple devices (DUTs) via multiple RF-to-DC converters in accordance with an embodiment of the present invention.

[0029] [Figure 8] 1 is a schematic electronic circuit diagram of a bipolar quantized superconducting current generator (QSG) according to an embodiment of the present invention.

[0030] [Figure 9A] 9 illustrates a dynamic simulation of the bipolar quantized superconducting current generator (QSG) shown in FIG. 8, according to an embodiment of the present invention. [Figure 9B] 9 illustrates a dynamic simulation of the bipolar quantized superconducting current generator (QSG) shown in FIG. 8, according to an embodiment of the present invention. [Figure 9C] 9 illustrates a dynamic simulation of the bipolar quantized superconducting current generator (QSG) shown in FIG. 8, according to an embodiment of the present invention. [Figure 9D] 9 illustrates a dynamic simulation of the bipolar quantized superconducting current generator (QSG) shown in FIG. 8, according to an embodiment of the present invention.

[0031] [Figure 10] 9 is a schematic diagram of a quantum mechanical system using the QSG shown in FIG. 8 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] FIG. 1 is a schematic electronic circuit diagram 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 current (DC) input port 102 and a radio frequency (RF) input port 104. The converter 100 also includes a direct current (DC)-to-single flux quantum (SFQ) (DC / SFQ) converter 106 connected to the RF input port 104. The DC-SFQ converter 106 is configured to convert RF current into SFQ current pulses. The radio frequency (RF)-to-direct current (DC) converter 100 also includes a Josephson junction (JJ) 108A connected to the DC input port 102 via a first inductive wire 110, to the DC-SFQ converter 106 via a second inductive wire 112, and to ground 116. The converter 100 also includes a resistor 118 connected to the Josephson junction (JJ) 108A and the DC input port 102 via a third inductive wire 120.

[0033] In operation, when a DC current is applied through DC input port 102, the DC current is shunted to ground 116 through JJ 108A, and substantially no DC current flows through resistor 118; when an RF current is applied through RF input port 104, an output train of SFQ current pulses from DC-SFQ converter 106, with an inter-pulse spacing that is inversely proportional to the RF current frequency, causes Josephson junction (JJ) 108A to switch at a rate equal to the RF frequency of the RF current, thereby generating a steady-state voltage across Josephson junction (JJ) 108A that is linearly dependent on the RF frequency, and as a result, the current flowing through resistor 118 depends directly 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 connected to the DC input port 102 via a first inductive wire 110, to the RF input port 104 via the DC-SFQ converter 106 via a second inductive wire 112, and to ground 116. While four Josephson junctions are illustrated in FIG. 1 , it will be understood that any number of Josephson junctions, e.g., two, three, or more, may be used. The plurality of Josephson junctions 108A, 108B, 108C, 108D are configured, when an RF current is applied via the RF input port 104, to switch at a rate comparable to the RF frequency of the RF current to produce a steady-state voltage across the plurality of Josephson junctions (JJs) 108A, 108B, 108C, 108D that is linearly dependent on the RF frequency, such that the current flowing through the resistor 118 depends directly on the RF frequency of the RF current. It may be worth noting that the more JJs used in an FJTL, the greater the amount of RF driven current the FJTL can supply.

[0035] 1, when a global bias current is applied to DC input port 102, current is completely shunted to ground (upward arrows) through JJs 108A, 108B, 108C, and 108D, and no current flows (downward arrows) through a resistive path (i.e., resistor 118) toward the device (DUT) (not shown). When RF current is applied at RF input port 104, JJs 108A, 108B, 108C, and 108D begin to switch at a rate comparable to the frequency of the applied RF tone, developing a steady-state voltage that is linearly dependent on the drive frequency. The FJTL varies with the RF frequency (f) across Josephson junctions (JJs) 108A, 108B, 108C, and 108D according to the following equation: clk ) to develop a steady-state DC voltage (V) proportional to V=Φ0×f clk where Φ is the superconducting magnetic flux quantum.

[0036] This voltage then drives a current through resistor 118, where the magnitude of the current is governed by Ohm's law: I=V / R=Φ×f clk / R. Thus, the last relationship shows that this circuit is a true RF frequency to DC current converter, where the linear scaling is set by the flux quantum and shunt resistance.

[0037] FIG. 2 is a current-voltage plot resulting from a simulation (e.g., using WRSpice) of 20 JJs (e.g., powered Josephson transmission lines—FJTLs) for different drive frequencies (the frequencies shown are 5 GHz, 7 GHz, 9 GHz, 11 GHz, 13 GHz, and 15 GHz) according to an embodiment of the present invention. In an embodiment, all JJs have a critical current of 250 μA, resulting in a total critical current for the circuit of 5 mA. FIG. 2 shows a Shapiro step starting at an applied DC bias of about 1.5 mA for the FJTLs at all applied frequencies. For example, when globally biased at a current of about 3.5 mA, the FJTLs can source or sink a current of up to about 1.5 mA and remain operational. The voltage developed across the FJTLs is extremely stable over a wide range of global bias currents.

[0038] 3 is a plot of output resistor current (in μA) versus time (in ns) obtained from a dynamic simulation (e.g., using WRSpice) of current driven through a series combination of a 130 pH inductor and a 0.1 resistor from a 20-JJ FJTL as a function of RF drive frequency, according to an embodiment of the present invention. WRSpice is a circuit simulation and analysis tool produced by Whiteley Research Incorporated. At time t=0 ns, a 5 GHz RF current is applied to the dc-to-SFQ converter 106. The output pulse from the converter 106 is then fed to the 20-JJ FJTL. The FJTL develops a voltage (at 5 GHz, this voltage is approximately 10 μV), which then drives a current through resistor 118 with a characteristic time of 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 is set back to 5 GHz, resulting in the current driven through resistor 118 returning to its original value of 100 μA.

[0039] 4 is a block diagram of a quantum mechanical system 200 including an RF-DC converter 100, according to an embodiment of the present invention. The quantum mechanical system 200 includes the RF-DC converter 100, which may be provided with, for example, one or more Josephson junctions JJ 108A, 108B, 108C, 108D. In an embodiment, the quantum mechanical system 200 also includes at least one quantum mechanical device 202 connected to the resistor 118 of the RF-DC converter 100. In an embodiment, the one or more devices 202 include at least one of a qubit, a superconducting quantum interference device, or a non-quantum mechanical device, such as, for example, a transistor or other circuit.

[0040] In embodiments, it may be beneficial to be able to increase the operating voltage of the FJTL. To increase the operating voltage, the quantum mechanical system 200 may include one or more rapid single flux quantum (RSFQ) pulse doubler stages 204. The one or more RSFQ pulse doubler stages 204 may be provided prior to the RF-to-DC converter 100, thereby increasing the operating voltage by two. m can be achieved, where m is the number of RSFQ pulse doubler stages.

[0041] 5 is a schematic electronic circuit diagram of an exemplary conventional rapid single flux quantum (RSFQ) pulse doubler 204. The RSFQ pulse doubler 204 has an input port 502 and an output port 504. The output port 504 of the RSFQ pulse doubler 204 is connected to the input port 104 of the DC-SFQ converter 100. The RSFQ pulse doubler 204 is configured to generate a single flux quantum (SFQ) pulse current input through the input port 104 of the DC-SFQ converter 100. However, other types of RSFQ pulse doublers may also be used.

[0042] FIG. 6 is a plot of a single pulse input to RSFQ pulse doubler 204 and multiple pulses output by RSFQ pulse doubler 204 according to an embodiment of the present invention. In an embodiment, the RSFQ pulse doubler 204 is configured to generate multiple current pulses 604 from a single radio frequency current pulse 602 input at an input port of the RSFQ pulse doubler 204 at twice the rate of the applied SFQ pulse at an output port of the RSFQ pulse doubler 204, thereby generating a larger voltage across the converter 100. In an embodiment, m stages of serially connected rapid single flux quantum (RSFQ) pulse doublers 204 can be used. For example, Figure 6 shows simulation results (e.g., using WRSpice) of the RSFQ pulse doublers 204 shown in Figure 5 cascaded five times in series. The m stages of the RSFQ pulse doublers 204 can be configured to generate an RF current (I) given by the following equation: I=2 m ×Φ0×f clk / R where Φ is the superconducting flux quantum and f clk is the RF frequency of the RF current, and R is the resistance of the resistor.

[0043] In an embodiment, when an input pulse arrives at input port 502, Josephson junctions J1 and J2 switch sequentially. The SFQ pulse from J2 is split between an upper path formed by Josephson junctions J4 and J5 and a lower branch formed by Josephson junctions J2 and J3. A shunt resistor Rs in the lower branch sets the L / R rise time of the current in the lower branch, delaying any switching action in Josephson junction J3. The upper branch pulse switches Josephson junction J5, which provides a pulse to output port 504 while also driving current into Josephson junctions J3 and J4. This additional current, along with that from the delayed current from the switching of Josephson junction J2, forces Josephson junction J3 to switch, generating a second pulse at the output. Josephson junction J4 acts as a guard junction to prevent Josephson junction J2 from switching twice. For m stages arranged in series, the resulting current driven by RF-DC converter 100 is I=2 m ×Φ0×f clk / R. This circuit and its operation are from existing literature. Is it a problem?

[0044] 7 is a schematic diagram illustrating how a single dc / SFQ converter 106 can controllably provide fast magnetic flux bias to multiple devices (DUTs) via multiple RF-DC converters in accordance with an embodiment of the present invention. In an embodiment, a 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 one of the multiple RF-DC converters 100. The multiple RF-DC converters 100 are addressable, so that SFQ pulses generated from RF current by the DC-SFQ converter 106 can be routed to a desired converter in the multiple RF-DC converters (FJTL) 100.

[0045] In an embodiment, the quantum mechanical system 200 further includes an input port 702 configured to receive direct current (DC) and radio frequency (RF) currents, 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 converter in the plurality of radio frequency (RF) to direct current (DC) converters (FJTL) 100 is connected to a corresponding one of the at least one demultiplexer (DEMUX) 706.

[0046] In an embodiment, a demultiplexer (DEMUX) 706A on a first address line 704A is connected to two demultiplexers (DEMUX) 706 on a 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 (FJTL) 100.

[0047] Thus, in an embodiment, a series combination of a multi-stage RSFQ pulse multiplier 204 and a resistive shunt FJTL 100 can be placed at the end of an RSFQ DEMUX tree, such that a single dc / SFQ converter source 106 can drive multiple devices (DUTs) 202. As shown in Figure 7, the single DC / SFQ converter 106 drives the input of a flux-biased 1:2 DEMUX 706. Depending on the sign of the current in each address line 704, the flux pulses from the DC / SFQ converter 106 are routed to either the left or right of the 1:2 DEMUX 704.

[0048] 8 is a schematic electronic circuit diagram of a bipolar quantized superconducting current generator (QSG) 800 according to an embodiment of the present invention. The bipolar quantized superconducting current generator (QSG) 800 includes a first input port 802 configured to receive at least one incrementing single flux quantum pulse and a second input port 804 configured to receive at least one decrementing single flux quantum pulse. The QSG 800 further 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 and second Josephson junctions 806, 808 are further connected to ground 809. The QSG 800 also includes an inductor (L) connected to the first Josephson junction 806 and the second Josephson junction 808. q ) 810. Inductor (L q ) 810 and the first and second Josephson junctions (JJs) 806 and 808 form a superconducting quantum interference device (SQUID) loop. During operation, the first Josephson junction 806 and the second Josephson junction 808 and the inductor (L q ) 810 and the current circulating in the storage SQUID loop gradually increases or decreases based on at least one increment single flux quantum pulse input through the first input port 802 or at least one decrement single flux quantum pulse input through the second input port 804, respectively.

[0049] In an embodiment, the current circulating in the storage SQUID loop is given by the following equation: ΔI=Φ0 / L q It is increased or decreased by a current increment ΔI given by, where Φ is the superconducting flux quantum and L q is the inductor (L q ) is the inductance value.

[0050] In an embodiment, the QSG 800 also includes a third input port 813 connected to the first Josephson junction (JJ) 806, the second Josephson junction (JJ) 808, and the inductor (Lq) 810. The third input port 813 is configured to input a bias direct current (DC) into the storage loop to electrically bias the first and second Josephson junctions 806 and 808 such that the first and second Josephson junctions 806 and 808 generate pulses when the pulses are applied to their respective inputs.

[0051] In an embodiment, the screening parameter β of the SQUID loop L depends on the critical current I of the first and second Josephson junctions 806 and 808 in the SQUID loop and the inductance value of the inductor connecting the first and second Josephson junctions.

[0052] In an embodiment, the QSG 800 further includes a third Josephson junction (JJ) 812 connected to the first Josephson junction (JJ) 806 and the first input port 802 via a first inductive line 816. The QSG 800 also includes a fourth Josephson junction (JJ) 814 connected to the second Josephson junction (JJ) 808 and the second input port 804 via a second inductive 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.

[0053] In an embodiment, when an SFQ pulse arrives at the first input port "Inc" 802, it triggers the switching of junctions J1 812 and J2 806, setting up a circulating current (arrow from left to right) flowing from J2 806 through Lq 810. The user can unset this circulating current by triggering junctions J3 808 and J4 814 from the second input port "Dec" 804, causing a current to circulate (arrow from right to left) flowing from J3 808 through Lq 810, and resetting the device. The induction value L q (Therefore, β l ) is so large that the circulating current is not large enough to over- or under-bias either the J3 808 or J2 806 junction, allowing multiple pulses to be applied consecutively from either the first input port "Inc" 802 or the second input port "Dec" 804. The SFQ pulses loaded from the first input port 802 or the second input port 804, respectively, have a circulating current of ΔI=Φ / L q in units of L q and increases or decreases the current in the storage loop formed by junctions J2 806 and J3 808. In an embodiment, β L is approximately equal to 100.

[0054] Therefore, the storage inductors L in combination with the last stages JJ (in this case, J2 806 and J3 808) of the first Josephson transmission line (JTL) 819 and the second Josephson transmission line (JTL) 820, respectively, q is, for example, approximately equal to 100. L This allows for the storage of a large number of flux quanta that can be loaded from either JTL (first JTL 819 or second JTL 820), which results in a step size ΔI=Φ / L q With current L q The correct amount of current flows through L as determined by the user. q Once loaded, the circuit can be powered down with the flux permanently stored in the loop. q It can support 100-1000 flux quantum values of circulating current depending on the value of Φ, thus allowing precise steps in flux bias on the order of 0.01-0.001Φ.

[0055] 9A-9D show dynamic simulations of the bipolar quantized superconducting current generator (QSG) 800 shown in FIG. 8, in accordance with an embodiment of the present invention. As a pulse such as that shown in FIG. 9A is loaded from the input of the second input port “Dec” 804, the current I(L q ) is the quantized quantity Φ0 / L as shown in FIG. q As a pulse such as that shown in FIG. 9C is loaded into the first input port "Inc" 802, the current increases by the same quantized amount with each flux pulse (a step-like portion rising from left to right), as shown in FIG. 9D. The SFQ pulse applied to the first input port "Inc" 802 increases the current stored in the loop by a quantized amount. The transition from one step to the next occurs as the pulse is applied. The SFQ pulse shown in FIG. 9C applied to the second input port 804 increases the current stored in the loop by a quantized amount, as shown in FIG. 9D. qThe current stored in decreases by a quantized amount (the step-like portion descending from left to right).

[0056] FIG. 10 is a schematic diagram of a quantum mechanical system 1000 using the QSG 800 shown in FIG. 8 according to an embodiment of the present invention. The quantum mechanical system 1000 includes a bipolar quantized superconducting current generator (QSG) 800. In an embodiment, the quantum mechanical system includes a plurality of QSGs 800. In an embodiment, the quantum mechanical system further includes a plurality of quantum mechanical devices 1002. Each of the plurality of quantum mechanical devices 1002 is inductively coupled to a corresponding one of the plurality of QSGs 800, for example, via an inductance 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.

[0057] In an embodiment, the quantum mechanical system 1000 further includes an input port 1008 configured to receive direct current (DC) and single flux quantum (SFQ) radio frequency currents. The quantum mechanical system 1000 further 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 one of the at least one demultiplexer (DEMUX) 1012.

[0058] In an embodiment, a single DC / SFQ converter 1006 can provide a bipolar flux bias to many different qubits 1002. The polarity of the current on the 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 the final stage, the polarity of the current on the address line determines whether the pulse is provided to the first input port “Inc” 802 or the second input port “Dec” 804 of the corresponding QSG 800. When the QSG 800 is coupled to the SQUID loop of a superconducting qubit (QB) 1002, it can provide both a positive and a negative flux bias. The scaling in the number of devices (e.g., qubits) that can be biased in such an architecture with the number of address lines is 2. (n-1) where n is the number of address lines.

[0059] One advantage of using the current QSG800 is that it offers the ability to generate bipolar persistent currents with zero quiescent power dissipation, allowing for efficient flux biasing of the bias circuits within the cryostat at all temperature stages. Additionally, when combined with the added benefit of the DEMUX control signal, the QSG, along with the DEMUX configuration shown in Figure 10, provides a scalable path from room temperature to a DC flux biased quantum processor with 1000 devices (e.g., qubits) with an exponentially decreasing number of control lines used.

[0060] While the descriptions of various embodiments of the present invention have been presented for illustrative purposes, they 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 selected to best explain the principles of the embodiments, practical applications of or technical improvements to the technology found in the market, or to enable others skilled in the art to understand the embodiments disclosed herein. According to this specification, the following items are also disclosed. [Item 1] A direct current (DC) input port; a radio frequency (RF) input port; a direct current (DC) to single flux quantum (SFQ) converter connected to the RF input port, the DC to SFQ converter configured to convert RF current into SFQ current pulses; a Josephson junction (JJ) connected to the DC input port via a first inductive line and to the DC-SFQ converter via a second inductive line, and connected to ground; a resistor connected to the Josephson junction via a third inductive wire and connected to the DC input port; 1. A radio frequency (RF) to direct current (DC) converter comprising: In operation, when a DC current is applied through the DC input port, no DC current flows through the resistor, and when an RF current at an RF frequency is applied through the RF input port, a current that is directly dependent on the RF frequency flows through the resistor based on the SFQ current pulses from the DC-SFQ converter switching the JJ. Radio frequency (RF) to direct current (DC) converter. [Item 2] 2. The converter of claim 1, wherein when the RF current is applied via the RF input port, an output train of SFQ current pulses from the DC-SFQ converter having an inter-pulse spacing that is inversely proportional to the RF frequency causes the Josephson junctions (JJs) to switch at a rate equivalent to the RF frequency of the RF current, thereby generating a steady-state voltage across the Josephson junctions (JJs) that is linearly dependent on the RF frequency. [Item 3] a plurality of Josephson junctions connected to the DC input port via the first inductive wire, to the RF input port via the DC-SFQ converter via the second inductive wire, and to ground; 3. The converter of claim 1 or 2, wherein the plurality of Josephson junctions are configured, when the RF current is applied through the RF input port, to switch at a rate equivalent to the RF frequency of the RF current to produce a steady-state voltage across the plurality of Josephson junctions (JJs) that is linearly dependent on the RF frequency, such that the current flowing through the resistor is directly dependent on the RF frequency of the RF current. [Item 4] The steady-state voltage (V) across the Josephson junction (JJ) is given by the following equation: V=Φ 0 ×f clk According to the above RF frequency (f clk ) and is proportional to Φ 0 4. The converter according to any one of items 1 to 3, wherein is a superconducting flux quantum. [Item 5] A direct current (DC) input port; a radio frequency (RF) input port; a direct current (DC) to single flux quantum (SFQ) converter connected to the RF input port, the DC to SFQ converter configured to convert RF current into SFQ current pulses; a Josephson junction (JJ) connected to the DC input port via a first inductive line and to the DC-SFQ converter via a second inductive line, and connected to ground; a resistor connected to the Josephson junction via a third inductive wire and connected to the DC input port; 1. A quantum mechanical system comprising a radio frequency (RF) to direct current (DC) converter having: a quantum mechanical system in which, in operation, when a DC current is applied through the DC input port, the DC current is shunted to ground through the Josephson junction (JJ) and substantially no current flows through the resistor; and when an RF current is applied through the RF input port, the Josephson junction (JJ) switches at a rate comparable to an RF frequency of the RF current to produce a steady-state voltage across the Josephson junction (JJ) that is linearly dependent on the RF frequency, such that the current flowing through the resistor is directly dependent on the RF frequency of the RF current. [Item 6] Item 6. The quantum mechanical system of item 5, further comprising at least one quantum mechanical device connected to the resistor. [Item 7] 7. The quantum mechanical system of claim 6, wherein the at least one quantum mechanical device comprises at least one of a qubit, a superconducting quantum interference device, or a non-quantum mechanical device. [Item 8] a rapid single flux quantum (RSFQ) pulse doubler having an input port and an output port; The quantum mechanical system of any one of items 5 to 7, wherein the output port of the RSFQ pulse doubler is connected to the input port of the DC-SFQ converter, and the RSFQ pulse doubler is configured to generate an SFQ pulse current input through the input port of the DC-SFQ converter. [Item 9] 9. The quantum mechanical system of claim 8, wherein the RSFQ pulse doubler is configured to generate multiple current pulses from a single radio frequency current pulse input at the input port of the RSFQ pulse doubler at twice the rate of the applied SFQ pulses at the output port of the RSFQ pulse doubler, thereby generating a larger voltage across the converter. [Item 10] further comprising m stages of said rapid single flux quantum (RSFQ) pulse doubler connected in series; The m stages of the RSFQ pulse doubler are expressed by the following formula: I=2 m ×Φ 0 ×f clk / R and configured to generate the RF current (I) given by Φ 0 is the superconducting flux quantum, and f clk 10. The quantum mechanical system of item 8 or 9, wherein R is the RF frequency of the RF current, and R is the resistance of the resistor. [Item 11] a plurality of radio frequency (RF) to direct current (DC) converters; a plurality of quantum mechanical devices, each of the plurality of quantum mechanical devices connected to a corresponding one of the plurality of RF-DC converters; Furthermore, 11. The quantum mechanical system of any one of items 5 to 10, wherein the plurality of RF-DC converters are addressable, such that the SFQ current pulse generated from the RF current is routed to a desired converter within the plurality of RF-DC converters. [Item 12] an input port configured to receive the direct current (DC) and the radio frequency (RF) current; a plurality of address lines, each address line having at least one demultiplexer (DEMUX), the demultiplexer (DEMUX) for a first address line being connected to the input port; Furthermore, Item 12. The quantum mechanical system of item 11, wherein each converter in the plurality of radio frequency (RF)-to-direct current (DC) converters is connected to a corresponding one of the at least one demultiplexer (DEMUX). [Item 13] Item 13. A quantum mechanical system as described in Item 12, wherein the demultiplexer (DEMUX) on the first address line is connected to two demultiplexers (DEMUX) on the second address line, and each of the two demultiplexers is connected to at least two radio frequency (RF) to direct current (DC) converters. [Item 14] a first input port configured to receive at least one incrementing single flux quantum pulse; and a second input port configured to receive at least one decrementing single flux quantum pulse; 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 Josephson junction (JJ) and the second Josephson junction (JJ) being further connected to ground; An inductor (L) connected to the first Josephson junction and the second Josephson junction q )and A bipolar quantized superconducting current generator (QSG) comprising: The above inductor (L q ), the first Josephson junction (JJ), and the second Josephson junction (JJ) form a superconducting quantum interference device (SQUID) loop, and during operation, the first Josephson junction, the second Josephson junction, and the inductor (Lq a bipolar quantized superconducting current generator (QSG) in which a current circulating in a storage SQUID loop formed by the first input port and the second input port gradually increases or decreases based on the at least one increment single flux quantum pulse input through the first input port or the at least one decrement single flux quantum pulse input through the second input port, respectively. [Item 15] The current circulating in the storage SQUID loop is given by the following equation: ΔI=Φ 0 / L q The current is increased or decreased by a given increment ΔI, Φ 0 is the superconducting flux quantum, and L q is the inductor (L q Item 15. The bipolar quantized superconducting current generator (QSG) according to item 14, wherein the inductance value is [Item 16] 16. The bipolar quantized superconducting current generator (QSG) according to item 14 or 15, further comprising a third input port connected to the first Josephson junction (JJ), the second Josephson junction (JJ), and the inductor (Lq), wherein the third input port is configured to input a bias direct current (DC) to the storage SQUID 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. [Item 17] The screening parameter β of the above SQUID loop L 17. The bipolar quantized superconducting current generator (QSG) according to any one of items 14 to 16, wherein the critical current I of the first Josephson junction and the second Josephson junction in the SQUID loop depends on the inductance values of the inductors connected to the first Josephson junction and the second Josephson junction. [Item 18] a third Josephson junction (JJ) connected to the first Josephson junction (JJ) and the first input port via a first inductive wire; a fourth Josephson junction (JJ) connected to the second Josephson junction (JJ) and the second input port via a second inductive wire; Furthermore, 18. The bipolar quantized superconducting current generator (QSG) according to any one of items 14 to 17, wherein 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). [Item 19] a first input port configured to receive one or more increment single flux quantum pulses; and a second input port configured to receive one or more decrement single flux quantum pulses. 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 Josephson junction (JJ) and the second Josephson junction (JJ) being further connected to ground; An inductor (L) connected to the first Josephson junction and the second Josephson junction q )and 1. A quantum mechanical system comprising a bipolar quantized superconducting current generator (QSG) having: The above inductor (L q ), the first Josephson junction (JJ), and the second Josephson junction (JJ) form a superconducting quantum interference device (SQUID) loop, and during operation, the first Josephson junction, the second Josephson junction, and the inductor (L q ) and a current circulating in the storage SQUID loop formed by the first input port and the second input port is gradually increased or decreased based on the one or more increment single flux quantum pulses input through the first input port or the one or more decrement single flux quantum pulses input through the second input port, respectively. [Item 20] a plurality of bipolar quantized superconducting current generators (QSGs); a plurality of quantum mechanical devices, each of the plurality of quantum mechanical devices inductively coupled to a corresponding one of the plurality of QSGs; Furthermore, 20. The quantum mechanical system of claim 19, wherein the plurality of QSGs are addressable so that an input SFQ pulse is routed to a desired QSG within the plurality of QSGs. [Item 21] an input port configured to receive direct current (DC) and single flux quantum (SFQ) radio frequency current; Each address line has at least one demultiplexer (DEMUX), and the demultiplexer (DEMUX) for the first address line is connected to the input port. Furthermore, 21. A quantum mechanical system according to item 19 or 20, wherein each QSG is connected to a corresponding one of the at least one demultiplexer (DEMUX).

Claims

1. a direct current (DC) input port; a radio frequency (RF) input port; a direct current (DC) to single flux quantum (SFQ) converter connected to the RF input port, the DC to SFQ converter configured to convert a first RF current into SFQ current pulses; a Josephson junction (JJ) connected to the DC input port via a first inductive line and to the DC-SFQ converter via a second inductive line, and connected to ground; a resistor connected to the Josephson junction via a third inductive wire and to the DC input port; a rapid single flux quantum (RSFQ) pulse doubler having an input port and an output port for doubling the rate of pulses, wherein a second RF current is input from the input port of the RSFQ pulse doubler, and the output port of the RSFQ pulse doubler is connected to an input port of the DC-SFQ converter via the RF input port, and the RSFQ pulse doubler is configured to input a plurality of current pulses as the first RF current to the input port of the DC-SFQ converter and cause the DC-SFQ converter to generate the SFQ current pulses; 1. A radio frequency (RF) to direct current (DC) converter comprising: In operation, when a DC current is applied via the DC input port, no DC current flows through the resistor, and when the first RF current at an RF frequency is applied via the RF input port, a current that is directly dependent on the RF frequency flows through the resistor based on the SFQ current pulses from the DC-SFQ converter switching the JJ. Radio frequency (RF) to direct current (DC) converter.

2. 2. The converter of claim 1, wherein when the first RF current is applied via the RF input port, an output train of SFQ current pulses from the DC-SFQ converter having an inter-pulse spacing that is inversely proportional to the RF frequency causes the Josephson junction (JJ) to switch at a rate equal to the RF frequency of the first RF current, thereby generating a steady-state voltage across the Josephson junction (JJ) that is linearly dependent on the RF frequency.

3. a plurality of Josephson junctions connected to the DC input port through the first inductive wire and to the RF input port through the DC-SFQ converter through the second inductive wire, and connected to ground; 3. The converter of claim 1, wherein the plurality of Josephson junctions are configured, when the first RF current is applied through the RF input port, to switch at a rate comparable to the RF frequency of the first RF current to produce a steady-state voltage across the plurality of Josephson junctions (JJs) that is linearly dependent on the RF frequency, such that the current flowing through the resistor is directly dependent on the RF frequency of the first RF current.

4. The steady state voltage (V) across the Josephson junction (JJ) is given by the following equation: V=Φ ０ ×f ｃｌｋ According to the RF frequency (f ｃｌｋ ) and is proportional to Φ ０ 4. A converter according to claim 1, wherein is a superconducting flux quantum.

5. a direct current (DC) input port; a radio frequency (RF) input port; a direct current (DC) to single flux quantum (SFQ) converter connected to the RF input port, the DC to SFQ converter configured to convert a first RF current into SFQ current pulses; a Josephson junction (JJ) connected to the DC input port via a first inductive line and to the DC-SFQ converter via a second inductive line, and connected to ground; a resistor connected to the Josephson junction via a third inductive wire and connected to the DC input port; a radio frequency (RF) to direct current (DC) converter having a rapid single flux quantum (RSFQ) pulse doubler having an input port and an output port for doubling the rate of pulses, wherein a second RF current is input from the input port of the RSFQ pulse doubler, and the output port of the RSFQ pulse doubler is connected to an input port of the DC-SFQ converter via the RF input port, and the RSFQ pulse doubler is configured to input a plurality of current pulses as the first RF current to the input port of the DC-SFQ converter and cause the DC-SFQ converter to generate the SFQ current pulses; A quantum mechanical system comprising: a quantum mechanical system in which, during operation, when a DC current is applied through the DC input port, the DC current is shunted to ground through the Josephson junction (JJ) and substantially no current flows through the resistor; and when the first RF current is applied through the RF input port, the Josephson junction (JJ) switches at a rate comparable to an RF frequency of the first RF current to produce a steady-state voltage across the Josephson junction (JJ) that is linearly dependent on the RF frequency, such that the current flowing through the resistor is directly dependent on the RF frequency of the first RF current.

6. The quantum mechanical system of claim 5 further comprising at least one quantum mechanical device connected to the resistor.

7. The quantum mechanical system of claim 6 , wherein the at least one quantum mechanical device comprises at least one of a qubit or a superconducting quantum interference device.

8. The quantum mechanical system of claim 7 further comprising at least one non-quantum mechanical device connected to said resistor.

9. 9. The quantum mechanical system of claim 8, wherein the RSFQ pulse doubler is configured to generate, from a single radio frequency current pulse input at the input port of the RSFQ pulse doubler, the multiple current pulses at the output port of the RSFQ pulse doubler, having a rate twice that of the applied second RF current, thereby generating a larger voltage across the RF-DC converter.

10. further comprising m stages of said rapid single flux quantum (RSFQ) pulse doubler connected in series; The m stages of the RSFQ pulse doubler are expressed by the following formula: I=2 ｍ ×Φ ０ ×f ｃｌｋ / R and configured to generate an output current (I) of the RF-DC converter given by Φ ０ is the superconducting flux quantum, and f ｃｌｋ 10. The quantum mechanical system of claim 8 or 9, wherein: π is the RF frequency of the second RF current; and R is the resistance of the resistor.

11. a plurality of radio frequency (RF) to direct current (DC) converters; a plurality of quantum mechanical devices, each of the plurality of quantum mechanical devices connected to a corresponding one of the plurality of RF-DC converters; Furthermore, 11. The quantum mechanical system of any one of claims 5 to 10, wherein the plurality of RF-DC converters are addressable such that the SFQ current pulses generated from the first RF current are routed to a desired converter within the plurality of RF-DC converters.

12. an input port configured to receive the direct current (DC) current and the first radio frequency (RF) current; a plurality of address lines, each address line having at least one demultiplexer (DEMUX), the demultiplexer (DEMUX) for a first address line being connected to the input port; Furthermore, 12. The quantum mechanical system of claim 11, wherein each converter in the plurality of radio frequency (RF) to direct current (DC) converters is connected to a corresponding one of the at least one demultiplexer (DEMUX).

13. 13. The quantum mechanical system of claim 12, wherein the demultiplexer (DEMUX) on the first address lines is connected to two demultiplexers (DEMUX) on the second address lines, and each of the two demultiplexers is connected to at least two radio frequency (RF) to direct current (DC) converters.

14. Josephson junction (JJ) and a direct current (DC) to single flux quantum (SFQ) converter coupled to the Josephson junction (JJ), the direct current (DC) to single flux quantum (SFQ) converter transmitting SFQ current pulses to the Josephson junction to switch the Josephson junction (JJ) and convert a plurality of current pulses into the SFQ current pulses; a rapid single flux quantum (RSFQ) pulse doubler for doubling the rate of pulses, the RSFQ pulse doubler receiving a second RF current and coupled to the DC-SFQ converter, configured to input the plurality of current pulses to the DC-SFQ converter and cause the DC-SFQ converter to generate the SFQ current pulses, and controlling the Josephson junctions (JJs); A radio frequency (RF) to direct current (DC) converter comprising:

15. The DC-SFQ converter comprises:

15. The radio frequency (RF) to direct current (DC) converter of claim 14, wherein the plurality of current pulses, which are a first radio frequency (RF) current, are converted into SFQ current pulses, and the Josephson junctions (JJs) are switched at a rate equivalent to an RF frequency of the first RF current to generate a steady-state voltage across the Josephson junctions (JJs) that is linearly dependent on RF frequency.

16. Josephson junction (JJ) and a direct current (DC) to single flux quantum (SFQ) converter coupled to the Josephson junction (JJ), the direct current (DC) to single flux quantum (SFQ) converter transmitting SFQ current pulses to the Josephson junction to switch the Josephson junction (JJ) and convert a plurality of current pulses into the SFQ current pulses; a rapid single flux quantum (RSFQ) pulse doubler for doubling the rate of pulses, the RSFQ pulse doubler receiving a second RF current and coupled to the DC-SFQ converter, configured to input the plurality of current pulses to the DC-SFQ converter and cause the DC-SFQ converter to generate the SFQ current pulses, and controlling the Josephson junctions (JJs); A quantum mechanical system comprising a radio frequency (RF) to direct current (DC) converter comprising:

17. The DC-SFQ converter comprises:

17. The quantum mechanical system of claim 16, wherein the plurality of current pulses, which are a first radio frequency (RF) current, are converted into SFQ current pulses, and the Josephson junctions (JJs) are switched at a rate equivalent to an RF frequency of the first RF current to produce a steady-state voltage across the Josephson junctions (JJs) that is linearly dependent on RF frequency.

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