Quantum state tomography across the exceptional point in a single dissipative qubit

By M. Naghiloo, M. Abbasi, Y. Joglekar, Kater Murch. Nature Physics, 2019

464 citations recorded by the source corpus.

Open physical systems can be described by effective non-Hermitian Hamiltonians that characterize the gain or loss of energy or particle numbers from the system. Experimental realization of optical1–7 and mechanical8–13 non-Hermitian systems has been reported, demonstrating functionalities such as lasing14–16, topological features7,17–19, optimal energy transfer20,21 and enhanced sensing22,23. Such realizations have been limited to classical (wave) systems in which only the amplitude information, not the phase, is measured. Thus, the effects of a systems’s proximity to an exceptional point—a degeneracy of such non-Hermitian Hamiltonians where the eigenvalues and corresponding eigenmodes coalesce24–29—on its quantum evolution remain unexplored. Here, we use post-selection on a three-level superconducting transmon circuit to carry out quantum state tomography of a single dissipative qubit in the vicinity of its exceptional point. We observe the spacetime reflection symmetry-breaking transition30,31 at zero detuning, decoherence enhancement at finite detuning and a quantum signature of the exceptional point in the qubit relaxation state. Our experiments show phenomena associated with non-Hermitian physics such as non-orthogonality of eigenstates in a fully quantum regime, which could provide a route to the exploration and harnessing of exceptional point degeneracies for quantum information processing. The dynamics of a single dissipative qubit undergoing non-Hermitian quantum dynamics in the vicinity of an exceptional point is experimentally studied in a superconducting transmon circuit.

Subfields: Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/3d581752fcc8ad7299e01aa9868de7b2c3b3da1e

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In Atomic and Molecular Physics, and Optics

Citations in the corpus

Hybrid-Liouvillian formalism connecting exceptional points of non-Hermitian Hamiltonians and Liouvillians via postselection of quantum trajectories (2020, methodology): “[6], this procedure allows to study the emergence of HEPs also in quantum systems.”
Quantum exceptional points of non-Hermitian Hamiltonians and Liouvillians: The effects of quantum jumps (2019, background): “In these systems, the precise control of amplification, dissipation, and coupling strength in principle allows EPs to be attained and characterized in the full quantum regime [7,100].”
Entanglement Phase Transition Induced by the Non-Hermitian Skin Effect (2022, background): “Non-Hermitian systems have been realized in several open quantum systems, including atoms [53–55], photons [56–59], exciton-polaritons [60], electronic spins [61, 62], and superconducting qubits [63].”
Chiral control of quantum states in non-Hermitian spin–orbit-coupled fermions (2021, background): “Although recent works have explored non-Hermitian systems within a quantum framework [28] and have demonstrated the PT symmetrybreaking transition in non-Hermitian quantum systems, such as photons [29, 30], superconducting qubits [31], single electronic spins [32], exciton-polaritons [33], or atoms ”
Engineered dissipation for quantum information science (2022, background): “They can be combined with the coherent evolution, writing The non-Hermitian effective Hamiltonian, represents the evolution of the system conditioned on no jumps occurring 23,34,35 .”