A paper recently published in the journal Cryogenics investigated the viability of a memristor-based cryogenic programmable direct current (DC) source for scalable in-situ quantum-dot control.
Study: Towards scalable cryogenic quantum dot biasing using memristor-based DC sources. Image Credit: agsandrew/Shutterstock.com
Background
Quantum computing could transform many areas of technology and science with its potential breakthroughs. Among the various platforms being explored, silicon quantum dots offer significant advantages over traditional superconducting qubits. They provide longer coherence times and a smaller qubit pitch and can operate at temperatures as high as 4.2 K.
Millions of quantum error correction protocol-compatible physical qubits will be required to realize those breakthrough applications. Recent advances like large-scale qubit fabrication have contributed to scaling to millions of physical qubits. Yet, the linear approach utilized for controlling these quantum dots has emerged as a bottleneck that hinders the integration of a rising number of qubits seamlessly. Scaling the control electronics concurrently has become necessary to address this issue and ensure the quantum dot control method’s scalability.
Cryogenic Memristor-based DC Sources
Early scaling proposals have explored cryo-complementary metal–oxide–semiconductor (cryo-CMOS) technology, with a particular focus on mixed-signal solutions for state manipulation and readouts using cryogenic digital-to-analog converters (DACs) for pulse generation.
Cryogenic DACs that integrate switched capacitors monolithically have been introduced to enable in situ quantum dot gate biasing. While this approach offers the advantage of ultra-low power dissipation, it also has the drawback of requiring periodic capacitor charge refreshment to counteract leakage current and maintain voltage integrity.
To address this issue, a memristor-based biasing circuit can be employed, which mitigates volatility problems that can arise during quantum dot system scaling. This circuit leverages the non-volatility of titanium oxide memristors, consuming only a few milliwatts of power, which can be reduced to tens of microwatts using integrated circuits.
Although the behavior of titanium oxide-based memristors has been extensively studied at cryogenic temperatures—demonstrating analog programming with 4-bit memristors and DC resistive switching—the concept of a memristor-based DC source has yet to be experimentally demonstrated at these temperatures.
The Study
In this study, researchers presented the experimental results and discussed the scaling potential for such DC sources. Specifically, they studied a commercial, operational amplifier (OpAmp) AD8605-based transimpedance amplifier (TIA)’s cryogenic DC behavior between 1.2 K and 300 K.
Subsequently, they proposed a memristor-based DC source prototype using the cryo-compatible AD8605 OpAmp. The circuit was characterized at room temperature, which served as a performance benchmark, and at 1.2 K.
The researchers performed DC sweeps with a 10 mV resolution and a 250 mV voltage range to validate the memristor-based DC source’s tunability. Additionally, they investigated the output voltage stability to ensure that it did not change over time owing to memristor resistance drift.
Limitations in power consumption and voltage resolution using discrete components indicated the need for a fully scalable and integrated CMOS-based approach. Thus, researchers discussed the prototype’s stability and proposed a new design to decrease the overall footprint and power consumption. Specifically, they proposed monolithic co-integration of 65 nm CMOS circuitry and emerging non-volatile memories (eNVMs) for biasing a silicon quantum dot’s gates cooled to 4.2 K.
Importance of this Work
In this study, the researchers successfully validated the memristor-based cryogenic programmable DC source's viability for scalable in-situ quantum-dot control. The DC source prototype, utilizing a commercial discrete operational amplifier, was demonstrated to operate effectively down to 1.2 K.
At cryogenic temperatures, the AD8605 operational amplifier exhibited reduced voltage gain and increased current consumption. Despite these challenges, the integration of memristor devices with an operational amplifier allowed researchers to perform 0.25 V-DC sweeps at 1.2 K using only two memristors.
The DC source prototype showed minimal output drift of approximately 1 μV s⁻¹ at 1.2 K, underscoring its potential for quantum dot biasing. Notably, the memristor-based DC source exhibited an output voltage retention time longer than the coherence time of spin qubits, a significant advantage over switched-capacitor circuits.
To fulfill the baseline quantum dot biasing requirements, including a 1 mV resolution over a 1 V range, monolithically co-integrated memristors with advanced CMOS circuitry could be effectively utilized to enable low power dissipation per DC source within a small footprint, reducing the power consumption gap with switched-capacitors biasing circuits. Simulations displayed a decrease in footprint and power consumption, down to 10 μW per DC source, which enables the integration of almost one million eNVM-based DC sources at a dilution fridge’s 4.2 K stage, paving the way for near-term quantum computing applications on a large scale.
In conclusion, the findings of this study demonstrated the feasibility of using memristor-based DC sources to realize scalable cryogenic quantum dot biasing.
Journal Reference
Mouny, P. et al. (2024). Towards scalable cryogenic quantum dot biasing using memristor-based DC sources. Cryogenics, 142, 103910. DOI: 10.1016/j.cryogenics.2024.103910, https://www.sciencedirect.com/science/article/pii/S0011227524001309
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