Sub-MHz SWAP spectroscopy of two-level systems in superconducting qubits

Joaquin Minguzzi; John Clai Owens; Oskar Painter; Matthew H. Matheny; Loren J. Swenson

Home/Archive/arXiv

arXiv · 2610.11125

Sub-MHz SWAP spectroscopy of two-level systems in superconducting qubits

Joaquin Minguzzi·John Clai Owens·Oskar Painter·Matthew H. Matheny·Loren J. Swenson

View original source ↗Read source document ↗Export metadata ↓

Abstract

An outstanding challenge in superconducting quantum circuits is mitigating loss from two-level system (TLS) defects. SWAP spectroscopy with flux-tunable qubits can detect individual TLSs, but the Rabi chevrons that signal coherent exchange have been observed only for the most strongly coupled defects. Here, we introduce a sequence with fast flux pulses only at state preparation and readout, switched off during the energy-relaxation delay for finer frequency resolution and longer interaction times. We detect Rabi chevrons at swap rates as low as 0.1 MHz, an order of magnitude lower than previously reported. In the dressed-state picture, we fit the coherent swap oscillations to extract the TLS energy-relaxation time. These Rabi chevrons reveal coherent TLSs with a median energy-relaxation time of 10 microseconds, at coupling strengths previously associated with incoherent TLSs. The swap coherence times exceed the qubit T2* limited by flux noise, indicating that the dressed gap protects them from low-frequency 1/f noise.

Explore related subjects

quant-ph

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Joaquin Minguzzi, John Clai Owens, Oskar Painter, Matthew H. Matheny, Loren J. Swenson. 2026-10-08. Sub-MHz SWAP spectroscopy of two-level systems in superconducting qubits. https://arxiv.org/abs/2610.11125

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Entanglement Detection with Rotationally Covariant Measurements -- From Compton Scattering to Lemonade

The accurate and efficient detection of quantum entanglement remains a central challenge in quantum information science. In this work, we study the detection of entanglement of polarized photons for measurement devices that are specified by rotational covariance. We derive explicit positive operator-valued measures (POVMs) showing that any such (idealized) setting is classified by one real measurable parameter r. In particular, we give a POVM formulation of the Klein-Nishina formula for Compton scattering of polarized photons. We provide an SDP-based entanglement certification method with computable bounds that operates on the full measured statistics, also considering semi-device independent scenarios. Furthermore, we show that, while Bell violations are impossible with two rotationally covariant measurements, EPR steering can still be certified under one-sided symmetry constraints. Finally, we demonstrate how our approach can be applied by analyzing a rotationally covariant showcase experiment using scattered polarized light in a selection of soft drinks. Our results motivate further investigation of entanglement detection with lemonade- based detectors.

quant-ph↗

arXiv2026

Simulation of topological superconductors and their competing orders using photon-mediated interactions

Realizing and controlling the unconventional pairing featured by topological superconductors remains a central challenge. We introduce a cavity QED quantum simulator that engineers competing chiral $p_x+ip_y$ and $d_{x^2-y^2}+id_{xy}$ orders by tailoring cavity-mediated couplings between atomic pseudospins that emulate momentum-dependent pairing channels. The desired spatially inhomogeneous cavity-mediated couplings can be engineered in a 2D optical lattice using incommensurate cavity-lattice wavelengths naturally occurring in cavity QED systems. This minimal and fully tunable platform enables controlled state preparation and continuous measurement of superconducting order parameters. To probe this competition, the platform enables selective excitation and direct time-domain detection of Bardasis-Schrieffer modes---collective excitations of the subdominant pairing channel. The same competing channel can have an even stronger impact out of equilibrium, where a sudden quench can drive its growth and abruptly reshape the dominant superconducting order, despite the stability of the dominant order in equilibrium. Together, these results establish cavity QED as a controlled setting for revealing hidden competing orders and exploring nonlinear dynamics of topological superconductivity that remain elusive in solid-state and ultracold-atom systems.

quant-ph↗

arXiv2026

Contractivity of time-dependent driven-dissipative systems

Experimentally relevant quantum systems are frequently described by a time-dependent Lindblad master equation in which the dissipation due to interaction with an environment is fixed, but the experimenter has control over the Hamiltonian, which therefore can change with time. A fundamental question that is also of practical relevance is to determine when such systems invariably lose information about their initial state (are exponentially contractive independent of the Hamiltonian) or when the control can be used to prevent this loss of information to some degree. Here, we identify the necessary and sufficient criterion on the dissipator for Hamiltonian-invariant contractivity. If the dissipator does not fulfil this criterion, but by itself is exponentially contractive, we also establish exponential contractivity for sufficiently weak or slow drives and construct examples where strong or fast driving prevents exponential contraction.

quant-ph↗