Abstract
We describe an approach to the high-fidelity measurement of a superconducting qubit using an on-chip microwave photon counter. The protocol relies on the transient response of a dispersively coupled measurement resonator to map the state of the qubit to "bright" and "dark" cavity pointer states that are characterized by a large differential photon occupation. Following this mapping, we photodetect the resonator using the Josephson Photomultipler (JPM), which transitions between classically distinguishable flux states when cavity photon occupation exceeds a certain threshold. Our technique provides access to the binary outcome of projective quantum measurement at the millikelvin stage without the need for quantum-limited preamplification and thresholding at room temperature. We achieve raw single-shot measurement fidelity in excess of 98% across multiple samples using this approach in total measurement times under 500 ns. In addition, we show that the backaction and crosstalk associated with our measurement protocol can be mitigated by exploiting the intrinsic damping of the JPM itself.
Highlights
Accurate state measurement is critical to the implementation of quantum error correction [1], and global optimization of a large-scale quantum processor demands minimization of physical resources required for qubit measurement [2]
We have developed and characterized a fast, accurate state measurement technique for superconducting qubits using on-chip microwave photon counters
Our study of achievable measurement repetition rate revealed an anomalous source of loss associated with Josephson photomultiplier (JPM) tunneling events; this topic merits further investigation
Summary
Accurate state measurement is critical to the implementation of quantum error correction [1], and global optimization of a large-scale quantum processor demands minimization of physical resources required for qubit measurement [2]. The measurement protocol relies on the transient response of a dispersively coupled linear resonator to map the state of the qubit onto “bright” and “dark” cavity pointer states characterized by a large differential photon occupation [14,15] [Fig. 1(a)]. Following this mapping, we photodetect the resonator using the Josephson photomultiplier (JPM) [16,17], which operates as a threshold detector of microwave photon occupation [Fig. 1(b)]. VI, we conclude and discuss prospects for the construction of a scalable quantum-toclassical interface at millikelvin temperatures
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
