Array of Optical Transition-Edge Sensors Fabricated by Ion-Milling Process Evaluated with Microwave Multiplexer for 100 or More Sensors

The optical transition-edge sensor (TES) pushes the boundary on fault-tolerant photonic quantum computers and low-invasive bio-imaging systems. As these systems evolve, there is an increasing demand for using a TES array comprising many sensors, often exceeding one hundred. Critical temperature \(T_c\) of the TESes should be uniform to ensure that all TESes operate at the same bias point with a series-bias current. Using an ion-milling process, we fabricate new titanium-based TES arrays consisting of 40 TESes. Each TES has lateral dimensions of 15 µm \(\times \) 13 µm. Our microwave-multiplexing measurement with rf-SQUIDs confirms that 24 out of the 40 TESes exhibit \(T_\textrm{c} = (336 \pm 6)\,\textrm{mK}\) uniform enough to apply the common bias. The yield is still 60%; however, this is the first report on the \(T_\textrm{c}\) uniformity of the ion-milling-based TESes. Seven optical fibers are connected to TESes. Five out of the seven sensors show transition. They show energy resolution \(0.54 \le {\Delta }E\,(\textrm{eV}) \le 0.62\) without FRM. The best energy resolution achieved without flux ramp modulation is 0.54 eV for a signal at 0.80 eV.