Phase locking of a semiconductor double-quantum-dot single-atom maser

Abstract

We experimentally study the phase stabilization of a semiconductor double quantum dot (DQD) single atom maser by injection locking. A voltage-biased DQD serves as an electrically tunable microwave frequency gain medium. The statistics of the maser output field demonstrate that the maser can be phase locked to an external cavity drive, with a resulting phase noise L = -99 dBc/Hz at a frequency offset of 1.3 MHz. The injection locking range, and the phase of the maser output relative to the injection locking input tone are in good agreement with Adler's theory. Furthermore, the electrically tunable DQD energy level structure allows us to rapidly switch the gain medium on and off, resulting in an emission spectrum that resembles a frequency comb. The free running frequency comb linewidth is ≈ 8 kHz and can be improved to less than 1 Hz by operating the comb in the injection locked regime.

A low-noise on-chip coherent microwave source

“…29 (∼22 kHz). Such a narrow linewidth suggests potential for a noticeable improvement of phase stability over previous coherent cryogenic sources [24][25][26][27][28][29]41 .…”

“…To gain more understanding on possible limitations of the linewidth of the generated signal, we utilize the well-established injection locking technique 25,26,29,42 . Here, the frequency of the injection tone f inj is fixed to that of the free emission at a given bias, whereas the power P inj is swept.…”

“…Nevertheless, we note that L = −116 dBc/Hz at an offset frequency of 1 MHz is well below −99 dBc/Hz obtained by the quantum-dot-based on-chip microwave source studied in ref. 26 .…”

“…Subsequently, we confirm the applicability of the source for quantum coherent operations by measuring the phase noise of the oscillator output. We present the total phase noise spectrum up to large offset frequencies and evaluate its impact on the dephasing of an ideal qubit which has not been reported in previous experimental works on cryogenic sources [24][25][26][27][28][29] .…”

“…For typical solid-state quantum information processing applications operating in the sub-20 GHz band, the specific requirements are quite stringent: the on-chip microwave source should exhibit a very low power dissipation, long coherence time, and low noise. Some of the properties have been studied with several prototype devices based on quantum dots [24][25][26][27] and Josephson junctions 28,29 embedded in resonators. Similar designs can also find applications in generating non-classical radiation [30][31][32][33] .…”