用于mK温度下射频测量的量子顺电变容管
Quantum paraelectric varactors for radio-frequency measurements at mK temperatures
摘要：
射频反射测量允许对耦合到谐振电路的量子点装置中托管的电荷和自旋量子位进行快速且灵敏的电读出。然而，优化读出需要谐振器的频率调谐和阻抗匹配。这难以在检测电路中使用常规的基于半导体或铁电的变容二极管来实现，因为它们的性能在与固态量子器件相关的mK温度范围内显著降低。在这里，我们探索一种不同类型的材料，钛酸锶，一种量子顺电体，在低温下具有非常大的场可调介电常数。使用钛酸锶变容二极管，我们证明了完美的阻抗匹配和谐振器频率调谐在6 mK，并在此温度下的电容可调谐性，耗散损耗和磁场灵敏度的变容二极管的特征。我们表明，这使我们能够优化碳纳米管量子点器件的射频读出信噪比，以实现4.8 $μ$ e/Hz $^{1/2}$的电荷灵敏度和0.04 aF/Hz $^{1/2}$的电容灵敏度。
英文摘要：
Radio-frequency reflectometry allows for fast and sensitive electrical readout of charge and spin qubits hosted in quantum dot devices coupled to resonant circuits. Optimizing readout, however, requires frequency tuning of the resonators and impedance matching. This is difficult to achieve using conventional semiconductor or ferroelectric-based varactors in the detection circuit as their performance degrades significantly in the mK temperature range relevant for solid-state quantum devices. Here we explore a different type of material, strontium titanate, a quantum paraelectric with exceptionally large field-tunable permittivity at low temperatures. Using strontium titanate varactors we demonstrate perfect impedance matching and resonator frequency tuning at 6 mK and characterize the varactors at this temperature in terms of their capacitance tunability, dissipative losses and magnetic field sensitivity. We show that this allows us to optimize the radio-frequency readout signal-to-noise ratio of carbon nanotube quantum dot devices to achieve a charge sensitivity of 4.8 $μ$e/Hz$^{1/2}$ and capacitance sensitivity of 0.04 aF/Hz$^{1/2}$.
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