Researchers at Aalto University in Finland have, for the first time, used an ultra-sensitive heat detector to measure quantum bits, bypassing the limitations of Heisenberg's uncertainty principle. They demonstrated that using a radiation heat meter as an ultra-sensitive heat detector can accurately read quantum bits in a single shot, with power consumption one-ten-thousandth of that of typical parametric amplifiers.
The Heisenberg uncertainty principle dictates that it is impossible to simultaneously know the precise position and momentum, voltage and current of a signal. Hence, it applies to quantum bit measurements using parametric voltage-current amplifiers. However, radiation heat detection is a completely different approach. When measuring power or photon numbers, a radiation heat meter does not require adding quantum noise originating from the Heisenberg uncertainty principle, as with parametric amplifiers. It delicately senses microwave photons emitted by quantum bits through minimally invasive detection interfaces.
Fidelity is a crucial metric physicists use to determine how accurately a device can detect the state of a quantum bit in a single measurement. In the experiment, the research team achieved a fidelity of 61.8% with a readout time of about 14 microseconds. When correcting for the energy relaxation time of the quantum bit, fidelity soared to 92.7%.
The researchers noted that with slight modifications, radiation heat meters could reach an ideal fidelity of 99.9% within 200 nanoseconds. Removing unnecessary components between the radiation heat meter and the chip not only significantly improves readout fidelity but also makes the measurement apparatus smaller and simpler, thereby making it more feasible to scale up to a higher number of quantum bits.
