Our publications
2026
by Fernando Valadares, Aleksandr Dorogov, Tanjung Krisnanda, May Chee Loke, Ni-Ni Huang, Pengtao Song, Yvonne Y. Gao
we integrate an on-chip flux-control architecture with a long-lived bosonic memory housed in a 3D superconducting cavity to dynamically access resonant Jaynes-Cummings (JC) interactions, and realize efficient arbitrary rotations between any pair of Fock levels in the memory. This on-demand access to JC interactions offers a versatile toolbox for implementing robust Fock-basis qudits and harnessing the rich dynamics of high-dimensional bosonic elements for quantum information processing!
by Tanjung Krisnanda, Fernando Valadares, Kyle Timothy Ng Chu, Pengtao Song, Adrian Copetudo, Clara Yun Fontaine, Lukas Lachman, Radim Filip, Yvonne Y. Gao
In this experiment, we introduce the Optimized Routine for Estimation of any Observable (OREO), a numerically optimized protocol that maps the expectation value of arbitrary oscillator observables onto a transmon state for efficient single-shot measurement. We demonstrate OREO in a bosonic cQED system as a means to efficiently measure phase-space quadratures and their higher moments, directly obtain faithful non-Gaussianity ranks, and effectively achieve state preparation independent of initial conditions in the oscillator!
2025
by Tanjung Krisnanda, Clara Yun Fontaine, Adrian Copetudo, Pengtao Song, Kai Xiang Lee, Ni-Ni Huang, Fernando Valadares, Timothy C. H. Liew, Yvonne Y. Gao
In this experiment, we implemented a simple and effective tomography scheme for continuous-variables by optimally sampling the excitation numbers in the cavity. Our method, called ORENS (Optimal Reconstruction via Excitation Number Sampling), outperforms the standard Wigner tomography in cQED and is much more generally applicable to other bosonic systems!
by Xiaozhou Pan, Tanjung Krisnanda, Andrea Duina, Kimin Park, Pengtao Song, Clara Yun Fontaine, Adrian Copetudo, Radim Filip, Yvonne Y. Gao
We developed a generalised strategy to perform effective quantum metrology using a single bosonic mode. In the experiment, we show that this protocol is not only versatile, allowing sensitive detection of phase and amplitude variations, but also highly adaptable, enabling us to optimise for the intended metrological goal on demand.
by Tanjung Krisnanda, Pengtao Song, Adrian Copetudo, Clara Yun Fontaine, Tomasz Paterek, Timothy C. H. Liew, Yvonne Y. Gao
We experimentally demonstrate a quantum reservoir processing approach for continuous-variable state reconstruction on a bosonic circuit quantum electrodynamics platform. The scheme learns the true dynamical process through a minimum set of measurement outcomes of a known set of initial states. We show that the map learnt this way achieves high reconstruction fidelity for several test states, offering significantly enhanced performance over using map calculated based on an idealised model of the system.
by Aniket Chaterjee, Jonathan Schwinger, Yvonne Y. Gao.
We harness model-free reinforcement learning (RL) together with a tailored training environment to achieve this multi-pronged optimization task. We demonstrate on the IBM quantum device that the measurement pulse obtained by the RL agent not only successfully achieves state-of-the-art performance, with an assignment error, but also executes the readout and the subsequent resonator reset almost 3x faster than the system’s default process.
2024
by Fernando Valadares, Ni-Ni Huang, Kyle Chu, Aleksandr Dorogov, Weipin Chua, Lingda Kong, Pengtao Song, Yvonne Y. Gao
Our latest experimental work on integrating fast flux-tunability with high-Q bosonic cQED devices to harness the distinct interaction regimes of light and matter in a single hardware. It opens many new possibilities in quantum control, bosonic gates, and quantum simulation!
2023
Enhancing the coherence of cat states by phase-space compression
by Xiaozhou Pan, Jonathan Schwinger, Ni-Ni Huang, Pengtao Song, Weipin Chua, Fumiya Hanamura, Atharv Joshi, Fernando Valadares, Radim Filip, Yvonne Y. Gao
In qcrew’s first publication, we present a versatile technique for creating robust non-Gaussian continuous-variable resource states in a highly linear bosonic mode and manipulating their phase-space distribution to achieve enhanced resilience against photon loss.
by Adrian Copetudo, Clara Yun Fontaine, Fernando Valadares, Yvonne Y. Gao
An invited perspective article about the rapidly evolving field of bosonic cQED and its many exciting applications. We had a blast putting this together to share our thoughts about the achievements and challenges of the field, both on the scientific and human aspects.
Appl. Phys. Lett. 124, 080502 (2024) – pulished 22nd Feb 2023
2021
An invited tutorial that aims to provide an outline of the core techniques that underlie most cQED experiments and offer a practical guide for a novice experimentalist to design, construct, and characterize their first quantum device.
2020
An invited review article of the recent developments in quantum error correction with bosonic codes and the progress towards realising fault-tolerant quantum information processing in cQED.
The efficient simulation of molecular vibronic spectra and extraction of the corresponding Franck-Condon factors for photoelectron processes using circuit QED platform.
2019
Entanglement of bosonic modes through an engineered exchange interaction
Implementation of an expotential-SWAP unitary and demonstration of a deterministic entangling gate within quantum error correction codes.
Engineering bilinear mode coupling in circuit QED: Theory and experiment
Theoretical analysis and experimental verification of the characteristics of parametrically-activated SWAP gates between superconducting cavities.
2018
Deterministic teleportation of a quantum gate between two logical qubits
Demonstration of a teleported controlled-NOT (CNOT) gate between two robust and error-correctable modules quantum modules.
Programmable Interference between Two Microwave Quantum Memories
Realisation of a driven, time-dependent bilinear coupling that can be tuned to implement a robust 50∶50 beam splitter between stationary states stored in two superconducting cavities.
2017 & prior
A CNOT gate between multiphoton qubits encoded in two cavities
Demonstration of a controlled NOT (CNOT) gate between two multiphoton qubits in two microwave cavities via parametrically driving a single transmon ancilla, enabling a high-fidelity entangling operation.
Normal-metal quasiparticle traps for superconducting qubits
Theoretical construction and experimentally verification of a model for the effect of a single small trap on the dynamics of the excess quasiparticles injected in a transmon-type qubit as well as the performance of the trap as a function of several key parameters.
A Schrödinger cat living in two boxes
Realisation of a two-mode cat state of electromagnetic fields in two microwave cavities bridged by a superconducting artificial atom, which can also be viewed as an entangled pair of single-cavity cat states.
Suspending superconducting qubits by silicon micromachining
Development of a powerful technique for relieving aluminum 3D transmon qubits from a silicon substrate using micromachining. This technique is a high yield, one-step deep reactive ion etch that requires no additional fabrication processes.
Surface participation and dielectric loss in superconducting qubits
A comprehensive study of the energy relaxation times of superconducting transmon qubits in 3D cavities as a function of dielectric participation ratios of material surfaces, computed by a two-step finite-element simulation and experimentally varied by qubit geometry.
Measurement and control of quasiparticle dynamics in a superconducting qubit
Implementation of a contactless injection technique with unprecedented dynamic range to quantitatively probe the dynamics of quasiparticles in superconducting transmon qubits.
Non-Poissonian Quantum Jumps of a Fluxonium Qubit due to Quasiparticle Excitations
Measurement of the fluctuations in the number of quasiparticle excitations by continuously monitoring the spontaneous quantum jumps between the states of a fluxonium qubit.
SU(3) Quantum Interferometry with Single-Photon Input Pulses
Development of a framework for solving the action of a three-channel passive optical interferometer on single-photon pulse inputs to each channel using SU(3) group-theoretic methods, which can be readily generalized to higher-order photon-coincidence experiments.