Quantum jumps of sound
Researchers coupled a superconducting qubit dispersively to a nanomechanical resonator to observe discontinuous transitions in energy levels, effectively measuring mechanical energy directly. By performing repeated quantum nondemolition parity measurements, they successfully heralded single-phonon states with high fidelity. This demonstrates the ability to track phonon number in real-time using QND measurements, which is crucial for bosonic quantum error correction and sensing.