  Integrated photonics offers compact and stable manipulation of optical
signals in miniaturized chips, with the possibility of changing dynamically
their functionality by means of integrated phase shifters. Cryogenic operation
of these devices is becoming essential for advancing photonic quantum
technologies, accommodating components like quantum light sources, single
photon detectors and quantum memories operating at liquid helium temperatures.
In this work, we report on a programmable glass photonic integrated circuit
(PIC) fabricated through femtosecond laser waveguide writing (FLW) and
controlled by thermo-optic phase shifters both in a room-temperature and in a
cryogenic setting. By taking advantage of a femtosecond laser microstructuring
process, we achieved reliable PIC operation with minimal power consumption and
confined temperature gradients in both conditions. This advancement marks the
first cryogenically-compatible programmable FLW PIC, paving the way for fully
integrated quantum architectures realized on a laser-written photonic chip.
