Photos of the cryogen-free DR200 dilution refrigerator system suitable for qubit quantum-state measurements. (a) Front view. (b) Top view. The fridge is installed on an aluminum-alloy frame with double acoustic isolation from the ground using rubber stands and air springs. The turbo pump and rotary valve are mechanically decoupled from the fridge. The fridge is also electrically isolated from the pumps, the control instruments, and the gas lines. The thick red arrow in (b) indicates where an accelerometer sensor is placed for vibration measurement.
Schematic overall arrangement of the cryogen-free DR200 dilution refrigerator measurement system. (1) Aluminum-alloy frame; (2) PTR coldhead; (3) and (4) pumping line; (5) bellows assembly; (6) turbo pump; (7) rotary valve; (8) compressor; (9) forepump; (10) LN2 coldtrap; (11) PTR compressor; (12) and (13) electrically isolated gas line and connecters; (14) rubber stands; (15) air-spring system (optional); (16) sand bag; (17) trilayer μ-metal shielding. Thin blue lines represent the gas lines.
Velocity spectral density of the dilution refrigerator system measured under three conditions: The whole system is off (bottom line), only the turbo pump is on (middle line), and both the turbo pump and the PTR are on (top line), respectively. See text for measurement details. Peaks at 50 Hz and its harmonics and subharmonics are due to power line interference (not due to mechanical vibrations).
Diagram of the electronic measurement system. Typical three kinds of the measurement lines are shown starting from the left side of the diagram: The qubit flux bias and SQUID-detector current lines, the SQUID-detector voltage lines, and the microwave/fast-pulse lines.
Typical attenuation versus frequency characteristic of the copper powder filters. The attenuation at 120 MHz is about 3 dB, and is more than 60 dB above 1 GHz. The length of filter is 7 cm as is shown in the inset.
Noise characteristic of a voltage preamplifier with gain of 1000 made from two AD624 instrumentation amplifiers in series. The noise spectrum density is less than 10 nV rms/ (refer to input) above ∼10 Hz up to 100 kHz (flat part above 1.6 kHz not shown). The inset shows the final assembly (the longer one) together with that of an isolation amplifier with unity gain (the shorter one).
(a) Rabi oscillation measured from an rf-SQUID type phase qubit made of Al Josephson junction (symbols). The applied microwave frequency is ∼16 GHz and a decay time of 70 ns is obtained from the exponentially damped sinusoidal oscillation fit (line). (b) Rabi frequency versus microwave amplitude (symbols). The line is a guide to the eye.
(a) Ramsey fringe measured from an rf-SQUID type phase qubit made of Al Josephson junction (symbols). The applied microwave frequency is ∼16 GHz and a decay time of 38 ns is obtained from the exponentially damped sinusoidal oscillation fit (line). (b) Ramsey frequency versus detuning (symbols). The line is a guide to the eye.
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