Low Power Low Noise Electronics at Qubit Temperature

A processor assembly for a quantum computer that alleviates thermal management challenges in cryogenic environments. The assembly features a temperature gradient within the processor, with electrical connectors thermally anchored to a higher temperature stage than the quantum processor die. This design enables efficient thermal management while maintaining electrical connectivity, allowing for reliable operation of quantum computing systems at millikelvin temperatures.

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Superconducting device for controlling coupling strength between qubits in quantum computers. The device has a hotspot nanowire sandwiched between two adjacent qubits. The hotspot nanowire can be biased with a current below a critical value to keep it superconducting, allowing strong qubit coupling. But if the bias exceeds the critical value, the nanowire enters a high-resistance state, decoupling the qubits. This allows independent tuning of the coupling strength between qubits without affecting the resonator quality factor. The nanowire can be embedded in an etched hole in the substrate to isolate it. Gold layers on the nanowire sides prevent harmful effects. A bias current line underneath isolates the nanowire.

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Tuning physical characteristics of quantum devices like qubits to improve quantum computing performance. The technique involves using a voltage gain tuner with inductive coupling to the device's inductance, positioned on a current path connected to the device. Applying a flux bias to the tuner varies the voltage ratio between nodes separated by a capacitor. This effectively tunes the device's capacitance. By introducing the flux bias and controlling it based on measured capacitance differences, the device capacitance can be brought closer to target values. This allows dynamic in-situ tuning of qubit, coupler, and other capacitances during quantum computing processes.

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Thermalizing and attenuating control signals in quantum computing systems to mitigate signal noise and power levels inside cryogenic chambers. The technique involves splitting the control signals outside the cryogenic chamber using a directional coupler. One split signal goes to the quantum devices inside the chamber while the other return signal is transmitted back to the higher temperature environment. This allows thermalizing and attenuating the control signals before they enter the colder cryogenic environment.

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A cryogenic control system for quantum devices that uses a superconducting rigid-flex circuit to thermally isolate control electronics from qubit chips while enabling electrical connectivity. The system comprises a qubit plane with qubit chips connected to a first rigid circuit portion of the superconducting rigid-flex circuit, which is cooled to below 100 mK. A control system with control chips connected to a second rigid circuit portion of the superconducting rigid-flex circuit operates at a higher temperature (below 10 K), allowing for heat dissipation while maintaining thermal isolation from the qubit plane.

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Operating a set of qubits at cryogenic temperatures through a novel interconnect architecture that enables efficient cooling while maintaining quantum coherence. The system employs a substrate with integrated connectors that connect the cryogenic qubits to a separate substrate containing the control electronics. This configuration enables the cryogenic qubits to be cooled using a single cooling element, while the control electronics maintain optimal temperature conditions. The connectors are designed to minimize heat transfer between the cryogenic and control substrates, allowing the cryogenic qubits to be cooled below 2K while the control electronics operate at room temperature.

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A method for modifying the normal state resistance of a Josephson junction in a superconducting qubit by thermally annealing the junction using a heated element in proximity to the junction. The heated element is brought into contact or proximity with the junction, and the thermal energy transferred to the junction increases its normal state resistance. The method enables precise control over qubit frequencies, particularly in large-scale quantum computing architectures where frequency crowding is a significant challenge.

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Tuning the physical characteristics of quantum devices like qubits and couplers in a quantum processor to improve performance. The tuning is done by using voltage gain tuners that are inductively coupled to the device's current path and positioned between nodes separated by a capacitor. Applying a flux bias to these tuners varies the voltage ratio between the nodes and thereby changes the effective capacitance of the device. This allows dynamic capacitance tuning during quantum operations to optimize qubit performance, for example by compensating for persistence current effects in annealing qubits.

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Magnetic flux control system for superconducting quantum computing that enables precise and dynamic control of superconducting circuit parameters. The system generates controlled single-flux-quantum pulses, converts them into magnetic flux, and integrates the flux to define an integrated magnetic flux. This integrated flux is then used to control quantum computing circuit parameters, such as microwave resonance frequencies, through precise manipulation of the superconducting circuit's magnetic field. The system enables rapid, programmable control of the superconducting circuit's parameters, particularly for large-scale quantum computing applications where precise control of qubit energies and couplings is critical.

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A superconducting memory circuit that increases memory density while maintaining reliability and performance. The circuit includes segmented write-word lines with local write select circuits, reducing flux quanta required for write operations. The segmented architecture enables higher integration density and improved write select margins. The circuit also employs a power-signal propagation circuit to efficiently distribute superconducting signals across the memory array.

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A scalable quantum computing system that enables low-error quantum computing at scale by controlling fluxonium qubits using baseband magnetic flux pulses. The system comprises an array of coupled fluxonium qubits, each comprising a Josephson junction shunted by a capacitor and inductor, and a control module that applies magnetic flux pulses to the qubits based on digital control signals. The pulses induce entangling interactions between qubits, enabling two-qubit gates with high fidelity, and can be dynamically controlled to achieve desired quantum operations.

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Compensating unwanted variations in superconducting quantum processors caused by fabrication imperfections. The compensation involves actively adjusting parameters like inductance and capacitance to match between qubits and components. This is done using tunable couplers, tunable LC circuits, and controllable Josephson junctions. By selectively tuning these elements, discrepancies in characteristics like critical currents and capacitances can be balanced between qubits and couplers. This allows compensating for variations in fabrication that affect qubit behavior.

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A device for detecting RF-range photons, comprising a detection element cooled to a superconducting state, a cooling device, and a micro-ohmmeter. The detection element, composed of a Dirac semimetal such as cadmium arsenide, exhibits a surface state that can absorb RF-range photons. The cooling device cools the detection element to a temperature below 0.45 K, enabling detection of multiple incident photons through measurement of changes in the detection element's electrical resistance.

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Automatic real-time calibration of qubit chips in quantum computers to maintain fidelity of quantum gates during execution of algorithms. The calibration involves using sensors on some qubits to measure environmental effects, which are then fed into a machine learning engine to generate updated control parameters. These updated parameters are used to generate subsequent pulses to manipulate the qubit states. This allows dynamic calibration during algorithm execution to compensate for drifting gate fidelity due to environmental noise.

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Converting signals between frequency regimes like optical and microwave to enable efficient quantum computing with reduced losses and compactness compared to using microwave signals throughout. The conversion is done by a separate system that takes microwave control signals from the main control system and converts them to the desired frequency regime for sending to the quantum processing unit. This allows using lower loss, more compact optical or terahertz signals in the quantum hardware instead of microwave signals. The conversion system receives the microwave control signals, converts them, and sends the converted signals to the qubits.

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Scalable quantum computing with improved thermal management to enable controlling a large number of qubits at cryogenic temperatures. The approach involves using separate cooling systems for the qubits and control electronics to maintain a temperature gradient between them. This allows close integration of the qubits and control circuits without excessive heat dissipation. A thermal barrier isolates the qubits from the control electronics. The qubits are cooled to lower temperatures than the control circuits. Two independent dilution refrigerators provide optimized cooling for each device type. This allows scaling quantum devices with fewer wires and lower heat dissipation compared to conventional systems with a single refrigerator.

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High-density embedded broadside-coupled attenuators for reducing noise in control signals transmitted to superconducting qubits. The attenuators comprise a reflectively-terminated input line broadside-coupled to an output line, eliminating the need for a looped-back output line configuration that consumes excessive space. The reflectively-terminated input line causes control signals to reverse direction upon encountering a termination point, enabling near-end crosstalk to generate an attenuated signal in the output line without requiring a loop-back configuration.

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Reducing parasitic interactions between qubits in a quantum computing system by operating qubits at distinct frequency patterns, particularly during idling, measurement, and quantum logic gate operations. The system employs a qubit frequency control architecture that enables scalable and practical implementation of quantum computations, including surface code cycles, with reduced parasitic couplings between diagonally opposed qubits.

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A system for mitigating dispersion-induced distortion of baseband pulses in quantum computing applications, comprising a qubit device, a signal generator producing a radiofrequency signal, and an envelope detector converting the radiofrequency signal into a baseband signal. The envelope detector is coupled to the signal generator via a non-superconducting cable and to the qubit device via a superconducting cable, enabling radiofrequency-to-baseband conversion to reduce dispersion-induced distortion.

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Determining the temperature of superconducting quantum computing devices using on-chip resonators to enable autonomous temperature monitoring without affecting device performance. The technique involves measuring the frequency shift of superconducting resonators due to temperature-induced changes in kinetic inductance. By comparing the resonator's estimated frequency at a reference temperature to its operating frequency, the temperature can be determined without direct contact or thermal sensors. This allows accurate temperature monitoring for superconducting qubits, which is critical for maximizing qubit lifetime by operating at low temperatures.

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