Transition Edge Sensors for Active Energy Removal from Silicon Substrates

An excess of quasiparticles is suspected to be an important source of dissipation and decoherence in superconductive qubits. Equilibrium quasiparticle density is reached when creation and destruction rates are equal. Some sources of quasiparticles are very hard to eliminate (ie. cosmic muons). Quantum circuits can be designed for additional robustness to these sources of unwanted excitations. One technique is to include additional energy removal methods.

In standard setups, wirebonds provide a large thermal conductance between the silicon substrate and the bath (~100 nW/K per wirebond), but are located at the perimeter of the chip. Unwanted energy spreads through the chip before removal. To prevent this, transition edge sensors (TESs) can be included on chip for active energy removal. TESs are voltage-biased superconducting films that are widely used in microcalorimeters and microbolometers. Energy from phonons, photons, or particles warms the TES, causing its temperature and resistance to increase. Due to negative electro-thermal feedback, bias current and power decrease and the absorbed energy is removed from the circuit.

We have designed, constructed, and characterized a TES circuit for active energy removal. We measured the effective thermal conductance provided by the TES. The measured chip had a heater and two TES devices. We measured the response of the second TES to excess energy from the heater with the first TES on and off. The first TES removed excess energy produced by the heater.