3 research outputs found
High-frequency broadband laser phase noise cancellation using a delay line
Laser phase noise remains a limiting factor in many experimental settings,
including metrology, time-keeping, as well as quantum optics. Hitherto this
issue was addressed at low frequencies, ranging from well below 1 Hz to
maximally 100 kHz. However, a wide range of experiments, such as, e.g., those
involving nanomechanical membrane resonators, are highly sensitive to noise at
higher frequencies in the range of 100 kHz to 10 MHz, such as nanomechanical
membrane resonators. Here we employ a fiber-loop delay line interferometer
optimized to cancel laser phase noise at frequencies around 1.5 MHz. We achieve
noise reduction in 300 kHz-wide bands with a peak reduction of more than 10 dB
at desired frequencies, reaching phase noise of less than -160 dB (rad/Hz)
with a Ti:AlO laser. These results provide a convenient noise reduction
technique to achieve deep ground-state cooling of mechanical motion.Comment: 12 pages, 6 figure
Density-wave ordering in a unitary Fermi gas with photon-mediated interactions
A density wave (DW) is a fundamental type of long-range order in quantum
matter tied to self-organization into a crystalline structure. The interplay of
DW order with superfluidity can lead to complex scenarios that pose a great
challenge to theoretical analysis. In the last decades, tunable quantum Fermi
gases have served as model systems for exploring the physics of strongly
interacting fermions, including most notably magnetic ordering, pairing and
superfluidity, and the crossover from a Bardeen-Cooper-Schrieffer (BCS)
superfluid to a Bose-Einstein condensate (BEC). Here, we realize a Fermi gas
featuring both strong, tunable contact interactions and photon-mediated,
spatially structured long-range interactions in a transversely driven
high-finesse optical cavity. Above a critical long-range interaction strength
DW order is stabilized in the system, which we identify via its superradiant
light scattering properties. We quantitatively measure the variation of the
onset of DW order as the contact interaction is varied across the BCS-BEC
crossover, in qualitative agreement with a mean-field theory. The atomic DW
susceptibility varies over an order of magnitude upon tuning the strength and
the sign of the long-range interactions below the self-ordering threshold,
demonstrating independent and simultaneous control over the contact and
long-range interactions. Therefore, our experimental setup provides a fully
tunable and microscopically controllable platform for the experimental study of
the interplay of superfluidity and DW order.Comment: 11 pages, 7 figure
Optomechanical Response of a Strongly Interacting Fermi Gas
We study a Fermi gas with strong, tunable interactions dispersively coupled to a high-finesse cavity. Upon probing the system along the cavity axis, we observe a strong optomechanical Kerr nonlinearity originating from the density response of the gas to the intracavity field and measure it as a function of interaction strength. We find that the zero-frequency density response function of the Fermi gas increases by a factor of two from the Bardeen-Cooper-Schrieffer to the Bose-Einstein condensate regime. The results are in quantitative agreement with a theory based on operator-product expansion, expressing the density response in terms of universal functions of the interactions, the contact and the internal energy of the gas. This provides an example of a driven-dissipative, strongly correlated system with a strong nonlinear response, opening up perspectives for the sensing of weak perturbations or inducing long-range interactions in Fermi gases