Quantum diffusion of microcavity solitons

Abstract

Coherently-pumped (Kerr) solitons in an ideal optical microcavity are expected to undergo random quantum motion that determines fundamental performance limits in applications of soliton microcombs. Here, this diffusive motion and its impact on Kerr soliton timing jitter is studied experimentally. Typically hidden below technical noise contributions, the quantum limit is discerned by measuring counter-propagating solitons. Their relative motion features only weak interactions and also presents excellent common mode suppression of technical noise. This is in strong contrast to co-propagating solitons which are found to have relative timing jitter well below the quantum limit of a single soliton on account of strong mutual motion correlation. Good agreement is found between theory and experiment. The results establish the fundamental limits to timing jitter in soliton microcombs and provide new insights on multi-soliton physics.Recently, coherently pumped solitons 1,2 have been realized in optical microcavities 3 . Unlike earlier temporal optical solitons, these new solitons are able to regenerate through Kerr-induced parametric amplification 4,5 , and strong resonant build-up in the high-Q microcavity enables access to optical nonlinearity at low power levels 6 .

Fundamental optical linewidth of soliton microcombs

“…(6) and (7). Note that the fundamental linewidth induced by quantum-noise timing jitter in our SiN microcomb is more than one order of magnitude higher than what has been previously reported for silica microcombs [29], mainly due to the larger nonlinear coefficient of SiN. Hence, the quantum noise sets a relatively high bound to the lowest achievable fundamental linewidth in this platform.…”

“…In the studies of supercontinuum generation, quantum noise poses fundamental limitations in the achievable spectral coherence [26,27]. In soliton microcombs, the quantum noise sets a fundamental-limited timing jitter [28][29][30][31]. The timing jitter PSD, Q ( ), affects the optical frequency noise of the comb lines Δ , ( ) through…”

Got the quantum jitters

“…Bao and colleagues close their work by pointing out that resonators with low nonlinearity and low finesse would seem best suited for minimizing quantum jitter 1 . Interestingly, these characteristics point towards the macroscopic sibling of monolithic microresonators -the optical fibre ring resonator.…”

“…But beneath these many varied sources lurks one that is more fundamental, unavoidable and elusive than the others: the jitter associated with the peculiarities of quantum physics itself. Now, writing in Nature Physics, Chengying Bao and colleagues describe an experiment that has resolved the quantum-limited timing jitter of one of the most important optical technologies to emerge in the past decade 1 -the soliton microresonator frequency comb 2 .…”

“…A central conclusion that arises from all three of the recent studies 1,10,11 is that the analytical formula derived for quantum-limited jitter of soliton microcombs appears to be spot on. It is very satisfying to see a complex theoretical formula that emerges as a tour de force analysis of soliton jitter 7 be so unequivocally confirmed by three near-simultaneous experiments.…”