Scaling of quantum computers to fault-tolerant levels relies critically on the integration of energyefficient, stable, and reproducible qubit control and readout electronics.In comparison to traditional semiconductor-control electronics (TSCE) located at room temperature, the signals generated by rf sources based on Josephson-junctions (JJs) benefit from small device sizes, low power dissipation, intrinsic calibration, superior reproducibility, and insensitivity to ambient fluctuations.Previous experiments to colocate qubits and JJ-based control electronics have resulted in quasiparticle poisoning of the qubit, degrading the coherence and lifetime of the qubit.In this paper, we digitally control a 0.01-K transmon qubit with pulses from a Josephson pulse generator (JPG) located at the 3-K stage of a dilution refrigerator.We directly compare the qubit lifetime T 1 , the coherence time T * 2 , and the thermal occupation P th when the qubit is controlled by the JPG circuit versus the TSCE setup.We find agreement to within the daily fluctuations of ±0.5 μs and ±2 μs for T 1 and T * 2 , respectively, and agreement to within the 1% error for P th .Additionally, we perform randomized benchmarking to measure an average JPG gate error of 2.1 × 10 -2 .In combination with a small device size (< 25 mm 2 ) and low on-chip power dissipation ( 100 μW), these results are an important step toward demonstrating the viability of using JJ-based control electronics located at temperature stages higher than the mixing-chamber stage in highly scaled superconducting quantum information systems.
Scaling of quantum computers to fault-tolerant levels relies critically on the integration of energyefficient, stable, and reproducible qubit control and readout electronics.In comparison to traditional semiconductor-control electronics (TSCE) located at room temperature, the signals generated by rf sources based on Josephson-junctions (JJs) benefit from small device sizes, low power dissipation, intrinsic calibration, superior reproducibility, and insensitivity to ambient fluctuations.Previous experiments to colocate qubits and JJ-based control electronics have resulted in quasiparticle poisoning of the qubit, degrading the coherence and lifetime of the qubit.In this paper, we digitally control a 0.01-K transmon qubit with pulses from a Josephson pulse generator (JPG) located at the 3-K stage of a dilution refrigerator.We directly compare the qubit lifetime T 1 , the coherence time T * 2 , and the thermal occupation P th when the qubit is controlled by the JPG circuit versus the TSCE setup.We find agreement to within the daily fluctuations of ±0.5 μs and ±2 μs for T 1 and T * 2 , respectively, and agreement to within the 1% error for P th .Additionally, we perform randomized benchmarking to measure an average JPG gate error of 2.1 × 10 -2 .In combination with a small device size (< 25 mm 2 ) and low on-chip power dissipation ( 100 μW), these results are an important step toward demonstrating the viability of using JJ-based control electronics located at temperature stages higher than the mixing-chamber stage in highly scaled superconducting quantum information systems.
Scaling of quantum computers to fault-tolerant levels relies critically on the integration of energy-efficient, stable, and reproducible qubit control and readout electronics. In comparison to traditional semiconductor control electronics (TSCE) located at room temperature, the signals generated by Josephson junction (JJ) based rf sources benefit from small device sizes, low power dissipation, intrinsic calibration, superior reproducibility, and insensitivity to ambient fluctuations. Previous experiments to co-locate qubits and JJ-based control electronics resulted in quasiparticle poisoning of the qubit; degrading the qubit's coherence and lifetime. In this paper, we digitally control a 0.01~K transmon qubit with pulses from a Josephson pulse generator (JPG) located at the 3~K stage of a dilution refrigerator. We directly compare the qubit lifetime T1, coherence time T2∗, and thermal occupation Pth when the qubit is controlled by the JPG circuit versus the TSCE setup. We find agreement to within the daily fluctuations on ±0.5μs and ±2μs for T1 and T2∗, respectively, and agreement to within the 1\% error for Pth. Additionally, we perform randomized benchmarking to measure an average JPG gate error of 2.1×10−2. In combination with a small device size (<25~mm2) and low on-chip power dissipation (≪100μW), these results are an important step towards demonstrating the viability of using JJ-based control electronics located at temperature stages higher than the mixing chamber stage in highly-scaled superconducting quantum information systems.
Compared to traditional semiconductor control electronics (TSCE) located at room temperature, cryogenic single flux quantum (SFQ) electronics can provide qubit measurement and control alternatives that address critical issues related to scalability of cryogenic quantum processors. Single-qubit control and readout have been demonstrated recently using SFQ circuits coupled to superconducting qubits. Experiments where the SFQ electronics are co-located with the qubit have suffered from excess decoherence and loss due to quasiparticle poisoning of the qubit. A previous experiment by our group showed that moving the control electronics to the 3 K stage of the dilution refrigerator avoided this source of decoherence in a high-coherence 3D transmon geometry. In this paper, we also generate the pulses at the 3 K stage but have optimized the qubit design and control lines for scalable 2D transmon devices. We directly compare the qubit lifetime T1, coherence time T2∗ and gate fidelity when the qubit is controlled by the Josephson pulse generator (JPG) circuit versus the TSCE setup. We find agreement to within the daily fluctuations for T1 and T2∗, and agreement to within 10% for randomized benchmarking. We also performed interleaved randomized benchmarking on individual JPG gates demonstrating an average error per gate of 0.46% showing good agreement with what is expected based on the qubit coherence and higher-state leakage. These results are an order of magnitude improvement in gate fidelity over our previous work and demonstrate that a Josephson microwave source operated at 3 K is a promising component for scalable qubit control.
In the quest to build a fault-tolerant quantum computer, superconducting circuits based on Josephson junctions have emerged as a leading architecture. Coherence times have increased significantly over the last two decades, and processors with ∼ 50 qubits have been experimentally demonstrated. These systems traditionally utilize microwave frequency control signals, and heterodyne based detection schemes for measurement. Both of these techniques rely heavily on room temperature microwave generators, high-bandwidth lines from room temperature to millikelvin temperatures, and bulky non-reciprocal elements such as cryogenic microwave isolators. Reliance on these elements makes it impractical to scale existing devices up a single order of magnitude, let alone the 5-6 orders of magnitude needed for performing fault-tolerant quantum algorithms. Here, I present results that suggesting superconducting digital logic, namely Single Flux Quantum (SFQ) logic, can replace analog control and measurement techniques, avoiding the significant overhead involved. I describe a scheme for measuring qubits with a device known as a Josephson Photomultiplier (JPM), which crucially stores the result of a qubit measurement in a classical circulating supercurrent within the device and allows for integration with SFQ detection circuitry. This technique is experimentally demonstrated, with single-shot measurement fidelity of 92%. Two methods for accessing this measurement result are presented, one utilizing ballistic fluxons, and another utilizing flux comparison. Initial experimental results of the latter are presented. In addition, I describe a scheme for controlling qubits with sequences of digital SFQ pulses. This method is then used to control a qubit without a microwave signal generator, with results of an average single-qubit gate fidelity of around 95%. When combined, these techniques form a nearly fully digital interface to superconducting qubits, which could allow these systems to scale much more easily.
Quantum computers with thousands or millions of qubits will require a scalable solution for qubit control and readout electronics. Colocating these electronics at millikelvin temperatures has been proposed and demonstrated, but there exist significant challenges with power dissipation, reproducibility, fidelity, and scalability. In this article, we experimentally demonstrate the use of a Josephson arbitrary waveform synthesizer (JAWS) to generate control signals at 4 K and perform spectroscopy of two components of a typical superconducting quantum information system: a linear resonator and a (nonlinear) transmon qubit. By locating the JAWS chip at 4 K and a qubit at 0.1 K, the direct path for quasi-particle poisoning from the JAWS chip to the qubit is broken. We demonstrate the stable, self-calibrated, and reproducible output signal of the JAWS when operated in its quantum locking range, a feature that allows these synthesizers to be replicated and scaled in the cryostat, all with identical on-chip, quantized, outputs. This is a proof-of-concept demonstration to generate signals at 4 K using driven superconducting electronics to control qubits at lower temperatures.
Solid-state quantum bits (qubits) generally require cryogenic operating temperatures together with rapid voltage (or current) pulse generation for qubit control and readout. Conventionally this is achieved by generating the signals at 300 K, transmitting them along very long coaxial cables that span ges 4 m from 300 K to sub-K (30-500 mK) into a dilution refrigerator, and reading-out the final qubit states via similar lengths of cable. Here we fabricate the control-pulse generator circuits using a foundry-processed SOS-CMOS technology that is capable of operation down to sub-K temperatures so that control signals can be generated at cryogenic temperatures in the near vicinity of the qubits. We present two full-custom large-scale integrated (LSI) control-pulse generator circuits: (a) a mixed-mode; and (b) a digital design each comprising hundreds of devices, and show pulse characteristics at 4.2 K, demonstrating LSI circuit operation at low temperatures. The mixed-mode design showed lower power dissipation but had increasing jitter at longer dwell times. The digital design eliminated jitter but at the expense of increased power dissipation. Although power dissipation is higher in the digital design, it should be possible to thermally anchor such control circuits at the 1 K stage of a dilution refrigerator thereby minimizing heat propagation to the qubits.
Abstract Realizing a practically useful superconducting quantum computer will require a dramatic scale-up of quantum control electronics to meet the growth in required qubit counts. Conventional rack-based room-temperature control electronics impose severe constraints on wiring density, cost, and system footprint, creating a barrier to large-scale and fault-tolerant quantum computing. Here we demonstrate a hybrid quantum control architecture that combines cryogenic complementary metal-oxide semiconductor (cryo‑CMOS) application-specific integrated circuits (ASICs) for two‑qubit flux control with room‑temperature radio‑frequency electronics for single‑qubit control and readout. The resulting system achieves high density and scalable quantum control without compromising two‑qubit gate fidelity. Deployed on a 156‑qubit quantum processor, the cryo-CMOS subsystem achieves two‑qubit gate errors at the {10}^{-3} level, with a best randomized benchmarking error per gate of 8.4\times{10}^{-4}, stable operation over multi‑day timescales, and no measurable performance degradation as we increase the temperature of the cryo-CMOS ASICs from 7 to 20 K. Thermal analysis identifies cryo-CMOS chip operation near 20 K as a favorable regime, enabling efficient cooling of a large number of channels per cryostat. Compared against rack‑based flux-control, the cryo-CMOS subsystem achieves statistically indistinguishable two-qubit gate fidelities under matched gate settings and enables a tenfold improvement in system spatial footprint. These results establish cryo‑CMOS flux control as a practical and scalable foundation for large‑scale and fault-tolerant superconducting quantum systems.