High-fidelity detection of information encoded in bosonic modes: Part I*

Qubit measurements in a computational basis are a necessary component of quantum computation. Examples include measurement at the end of a quantum algorithm and projective measurements during teleported operations. Although qubit readout suffers from errors, they may be repeated if the readout is quantum non-demolition (QND). In this way, individual imperfect readouts can be combined via methods such as majority voting to form a more accurate measurement. The measurement fidelity will be limited, however, by state transitions between qubit basis states. For two-level qubits, a single relaxation event destroys the information in the qubit. An increased distance in the Hilbert space between basis states for qubits encoded in bosonic modes, however, exponentially suppresses this infidelity limit due to transitions. In this talk, we present a measurement scheme in the circuit quantum electrodynamics (cQED) platform that utilizes repeated QND readouts to suppress measurement infidelity due to both individual readout errors and relaxation. [1] We characterize the fidelity of this scheme in terms of experimental parameters for various encodings.

[1] Hann et al, PRA 98 022305