A Johnson noise thermometer (JNT) determines the thermodynamic temperature through cross-correlation measurement of the Johnson noise in a sense resistor at an unknown temperature. In the quantum voltage calibrated JNT system, a superconductive quantum voltage noise source (QVNS) is required to produce artificial pseudo-random noise to calibrate the gain of the cross-correlation electronics. In this paper, we present the design, fabrication, and characterization of the QVNS chip. Compared with our previous design, a new straightforward mirror symmetric layout is implemented. For this layout, the coplanar waveguides (CPWs) have the same lengths and transmission parameters. Equal pulse magnitudes are delivered to each Josephson junction array under the same output settings of the bipolar pattern generator. The modified QVNS chip is thereby enhanced because the quantum locking range is enlarged. A copper foil shielding package is used to eliminate crosstalk in this design. The first spectral comparison of two Josephson junction (JJ) arrays of with and without shielding is presented in this paper. The comparative results demonstrate that the shielding is effective. The abovementioned improvements enable us to synthesize both single and multitone waveforms with good spectral results, such that the chip satisfies the requirement of a QVNS-based JNT system for temperature measurements.
A microwave (MW) synthesizer is a key component of high-performance coherent population trapping (CPT) atomic clocks, which are competitive candidates as miniature, low-power-consumption atomic clocks. In this work, we demonstrated a microwave synthesizer and a self-adaption system to satisfy the requirement of short term and mid-long term frequency stability of CPT clocks. From the experimental results, the absolute phase noise of the microwave synthesizer was measured as -110 dBc/Hz at 200 Hz. The off-resonant light shift limitation for CPT clock can achieve better than 1 × 10 −14 based on our microwave synthesizer and self-adaption system. The proposed low-phase-noise microwave synthesizer and selfadaption system presented can also be used in other high-performance microwave atomic sensors and standards.
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