Quantum sensing in the infrared regime often demands the use of expensive and cryogenically operated detectors. Nonlinear interferometry has paved the way for information transfer from the infrared to the near--infrared or visible regime in various quantum technologies. A particularly interesting application of these interferometers involves spectrally--resolved quantum imaging using undetected photons, enabled by the use of temperature--tunable parametric amplifiers. In this work, we demonstrate spectrally resolved transmission imaging with undetected photons around 1550 nm using a spontaneous parametric down conversion based folded nonlinear interferometric scheme, registering the attenuation of a zebrafish larva as a biological feasibility test. We characterize and calibrate the interferometer, having achieved spectrally resolved interference fringes with a maximum baseline visibility of
∼74% in the near--infrared regime. Phase--stepped readout of a grating spectrometer gives a resolving power of
∼1460 (from the spectrometer's point spread function) at 1550 nm, and
∼730 from the coherence length, the finest reported for imaging with undetected photons, over an instantaneous spectral window of
≈51 cm
−1.
We evaluate the limiting imaging sensitivity of a two-dimensional faint phase object, placed within an interferometer. We consider the case when both input ports of the interferometer are illuminated by spatially multimode quadrature-squeezed light, and a differenced detection scheme where spatial resolution is used. This provides the Heisenberg-limited measurement sensitivity of the spatial phase distribution in the object. The optimum choise of space-time scales of the system and the resolving power of the measurement in space and time are discussed.
Abstract Large-scale atom interferometers promise unrivaled strain sensitivity to mid-band gravitational waves, and will probe a new parameter space in the search for ultra-light scalar dark matter. These proposals require gradiometry with kilometer-scale baselines, a momentum separation above 104ℏk between interferometer arms, and optical transitions to long-lived clock states to reach the target sensitivities. Prohibitively high optical power and wavefront flatness requirements have thus far limited the maximum achievable momentum splitting. Here we propose a scheme for optical cavity enhanced atom interferometry, using circulating, spatially resolved pulses, and intracavity frequency modulation to meet these requirements. We present parameters for the realization of 20 kW circulating pulses in a 1 km interferometer enabling 104ℏk splitting on the 698 nm clock transition in 87Sr. This scheme addresses the presently insurmountable laser power requirements and is feasible in the context of a kilometer-scale atom interferometer facility.