3 research outputs found
Erasure detection of a dual-rail qubit encoded in a double-post superconducting cavity
Qubits with predominantly erasure errors present distinctive advantages for
quantum error correction(QEC) and fault tolerant quantum computing. Logical
qubits based on dual-rail encoding that exploit erasure detection have been
recently proposed in superconducting circuit architectures, either with coupled
transmons or cavities. Here, we implement a dual-rail qubit encoded in a
compact, double-post superconducting cavity. Using an auxiliary transmon, we
perform erasure detection on the dual-rail subspace. We characterize the
behaviour of the codespace by a novel method to perform joint-Wigner
tomography. This is based on modifying the cross-Kerr interaction between the
cavity modes and the transmon. We measure an erasure rate of 3.981 +/- 0.003
(ms)-1 and a residual dephasing error rate up to 0.17 (ms)-1 within the
codespace. This strong hierarchy of error rates, together with the compact and
hardware-efficient nature of this novel architecture, hold promise in realising
QEC schemes with enhanced thresholds and improved scaling
Distinguishing parity-switching mechanisms in a superconducting qubit
Single-charge tunneling is a decoherence mechanism affecting superconducting
qubits, yet the origin of excess quasiparticle excitations (QPs) responsible
for this tunneling in superconducting devices is not fully understood. We
measure the flux dependence of charge-parity (or simply, ``parity'') switching
in an offset-charge-sensitive transmon qubit to identify the contributions of
photon-assisted parity switching and QP generation to the overall
parity-switching rate. The parity-switching rate exhibits a
qubit-state-dependent peak in the flux dependence, indicating a cold
distribution of excess QPs which are predominantly trapped in the low-gap film
of the device. Moreover, we find that the photon-assisted process contributes
significantly to both parity switching and the generation of excess QPs by
fitting to a model that self-consistently incorporates photon-assisted parity
switching as well as inter-film QP dynamics
Fully Directional Quantum-limited Phase-Preserving Amplifier
We present a way to achieve fully directional, quantum-limited
phase-preserving amplification in a four-port, four-mode superconducting
Josephson circuit by utilizing interference between six parametric processes
that couple all four modes. Full directionality, defined as the reverse
isolation surpassing forward gain between the matched input and output ports of
the amplifier, ensures its robustness against impedance mismatch that might be
present at its output port during applications. Unlike existing directional
phase-preserving amplifiers, both the minimal back-action and the
quantum-limited added noise of this amplifier remains unaffected by noise
incident on its output port. In addition, the matched input and output ports
allow direct on-chip integration of these amplifiers with other circuit QED
components, facilitating scaling up of superconducting quantum processors