Efficient decoupling of a non-linear qubit mode from its environment
Abstract: To control and measure the state of a quantum system it must necessarily be coupled to external degrees of freedom. This inevitably leads to spontaneous emission via the Purcell effect, photon-induced dephasing from measurement back-action, and errors caused by unwanted interactions with nearby quantum systems. To tackle this fundamental challenge, we make use of the design flexibility of superconducting quantum circuits to form a multi-mode element -- an artificial molecule -- with symmetry-protected modes. The proposed circuit consists of three superconducting islands coupled to a central island via Josephson junctions. It exhibits two essential non-linear modes, one of which is flux-insensitive and used as the protected qubit mode. The second mode is flux-tunable and serves via a cross-Kerr type coupling as a mediator to control the dispersive coupling of the qubit mode to the readout resonator. We demonstrate the Purcell protection of the qubit mode by measuring relaxation times that are independent of the mediated dispersive coupling. We show that the coherence of the qubit is not limited by photon-induced dephasing when detuning the mediator mode from the readout resonator and thereby reducing the dispersive coupling. The resulting highly protected qubit with tunable interactions may serve as a basic building block of a scalable quantum processor architecture, in which qubit decoherence is strongly suppressed.
- H. Häffner, C. Roos, and R. Blatt, Quantum computing with trapped ions, Physics Reports 469, 155 (2008).
- J. M. Raimond, M. Brune, and S. Haroche, Manipulating quantum entanglement with atoms and photons in a cavity, Rev. Mod. Phys. 73, 565 (2001).
- Google Quantum AI, Suppressing quantum errors by scaling a surface code logical qubit, Nature 614, 676 (2023).
- A. A. Clerk and D. W. Utami, Using a qubit to measure photon-number statistics of a driven thermal oscillator, Phys. Rev. A 75, 042302 (2007).
- G. Huber, in preperation.
- D. A. Lidar, I. L. Chuang, and K. B. Whaley, Decoherence-free subspaces for quantum computation, Phys. Rev. Lett. 81, 2594 (1998).
- R. H. Dicke, Coherence in spontaneous radiation processes, Phys. Rev. 93, 99 (1954).
- R. G. DeVoe and R. G. Brewer, Observation of superradiant and subradiant spontaneous emission of two trapped ions, Phys. Rev. Lett. 76, 2049 (1996).
- W. Guerin, M. O. Araújo, and R. Kaiser, Subradiance in a large cloud of cold atoms, Phys. Rev. Lett. 116, 083601 (2016).
- S.-Y. Zhu and M. O. Scully, Spectral line elimination and spontaneous emission cancellation via quantum interference, Phys. Rev. Lett. 76, 388 (1996).
- J. M. Gambetta, A. A. Houck, and A. Blais, Superconducting qubit with purcell protection and tunable coupling, Phys. Rev. Lett. 106, 030502 (2011).
- P.-M. Billangeon, J. S. Tsai, and Y. Nakamura, Scalable architecture for quantum information processing with superconducting flux qubits based on purely longitudinal interactions, Phys. Rev. B 92, 020509 (2015).
- S. Richer and D. DiVincenzo, Circuit design implementing longitudinal coupling: A scalable scheme for superconducting qubits, Phys. Rev. B 93, 134501 (2016).
- A. W. Cross and J. M. Gambetta, Optimized pulse shapes for a resonator-induced phase gate, Phys. Rev. A 91, 032325 (2015).
- B. Efron and R. Tibshirani, An Introduction to the Bootstrap (Chapman and Hall/CRC, 1994).
Paper Prompts
Sign up for free to create and run prompts on this paper using GPT-5.
Top Community Prompts
Collections
Sign up for free to add this paper to one or more collections.