Chasing higher qubit counts in near-term quantum computers requires constant engineering feats, with one major challenge being the measurement of qubits. Parametric amplifiers are traditionally used for this purpose, but they can introduce unwanted noise and potential decoherence of the qubits due to their amplification of weak signals. The QCD research group at Aalto University has shown that thermal bolometers can be used as ultra-sensitive detectors for qubit measurements. In a recent Nature Electronics paper, they demonstrated that bolometer measurements can be accurate enough for single-shot qubit readout, offering an alternative to traditional amplifiers.
The Heisenberg uncertainty principle dictates that one cannot simultaneously know certain pairs of properties with accuracy, such as a signal’s position and momentum. This limitation also applies to qubit measurements conducted with parametric voltage-current amplifiers. Bolometric energy sensing, on the other hand, provides a fundamentally different way of measuring qubits, bypassing Heisenberg’s rule. Bolometers subtly detect microwave photons emitted from the qubit with minimal interference, offering a smaller form factor compared to amplifiers and consuming significantly less power.
The QCD group’s experiments achieved a single-shot fidelity of 61.8%, with the potential to reach higher levels with modifications. By utilizing materials like graphene with lower heat capacity and removing unnecessary components in the setup, bolometers could approach 99.9% single-shot fidelity in a faster time frame. This improvement not only enhances readout fidelity but also simplifies the measurement device, making it more suitable for scaling up to higher qubit counts.
The QCD research group has showcased the potential of bolometers for ultrasensitive, real-time microwave measurements in previous studies, demonstrating their ability to shorten readout times to less than a microsecond. Collaborating with the Research Council of Finland Centre of Excellence for Quantum Technology and VTT Technical Research Centre of Finland, the group’s work has been funded by various grants and foundations, paving the way for advancements in quantum technology. With the continued development and refinement of bolometers for qubit measurements, the scalability and accuracy of quantum computers are poised to improve significantly in the near future.
