Quantum nondemolition measurement of microwave photons using engineered quadratic interactions
Chunqing Deng, Jay Gambetta, Adrian Lupaşcu · Physical Review B · 2010
We present a quantum electrical circuit with Josephson junctions formed of two anharmonic oscillators coupled with an interaction $g{\ensuremath{\gamma}}_{1}^{2}{\ensuremath{\gamma}}_{2}^{2}$, where ${\ensuremath{\gamma}}_{1}$ and ${\ensuremath{\gamma}}_{2}$ are positionlike coordinates. This type of coupling allows the quantum nondemolition measurement of the energy of one oscillator by monitoring the frequency of the second oscillator. Despite the fundamental tradeoff between the coupling strength $g$ and maximum photon-storage capacity of the oscillators, it is possible to achieve high-fidelity detection of up to ten photons over time scale on the order of microseconds. We discuss the possibility of observing quantum jumps in the number of photons and related applications.