两种异质结双极晶体管放大电路在毫开尔文温度下的单次读出性能
Single-Shot Readout Performance of Two Heterojunction-Bipolar-Transistor Amplification Circuits at Millikelvin Temperatures
摘要：
自旋量子位的高保真单次读出需要比自旋状态的T1时间快得多的区分状态。提高读出保真度和带宽（BW）的一种方法是低温放大，其中来自量子位的信号在引入噪声源之前被放大，并且室温放大器可以以较低的增益和较高的BW操作。我们比较了两种低温放大电路的性能：电流偏置异质结双极晶体管电路（CB-HBT），和交流耦合HBT电路（AC-HBT）。两个电路都安装在稀释制冷机的混合室级上，并连接到印刷电路板（PCB）上的硅金属氧化物半导体（Si-MOS）量子点器件。CB-HBT的功耗范围为0.1至1 μW，而AC-HBT的功耗范围为1至20 μW。就输入而言，两个电路的噪声频谱密度都很低，在15至30 fA/ $\sqrt{\textrm{Hz}}$范围内。CB-HBT和AC-HBT的电荷灵敏度分别为330 μe/ $\sqrt{\textrm{Hz}}$和400 μe/ $\sqrt{\textrm{Hz}}$。对于所执行的单次读出，两个电路实现低于$10^{-3}$的误比特率所需的时间小于10 μs，该误比特率是量子纠错的假定阈值。
英文摘要：
High-fidelity single-shot readout of spin qubits requires distinguishing states much faster than the T1 time of the spin state. One approach to improving readout fidelity and bandwidth (BW) is cryogenic amplification, where the signal from the qubit is amplified before noise sources are introduced and room-temperature amplifiers can operate at lower gain and higher BW. We compare the performance of two cryogenic amplification circuits: a current-biased heterojunction bipolar transistor circuit (CB-HBT), and an AC-coupled HBT circuit (AC-HBT). Both circuits are mounted on the mixing-chamber stage of a dilution refrigerator and are connected to silicon metal oxide semiconductor (Si-MOS) quantum dot devices on a printed circuit board (PCB). The power dissipated by the CB-HBT ranges from 0.1 to 1 μW whereas the power of the AC-HBT ranges from 1 to 20 μW. Referred to the input, the noise spectral density is low for both circuits, in the 15 to 30 fA/$\sqrt{\textrm{Hz}}$ range. The charge sensitivity for the CB-HBT and AC-HBT is 330 μe/$\sqrt{\textrm{Hz}}$ and 400 μe/$\sqrt{\textrm{Hz}}$, respectively. For the single-shot readout performed, less than 10 μs is required for both circuits to achieve bit error rates below $10^{-3}$, which is a putative threshold for quantum error correction.
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