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Observing Interferences between Past and Future Quantum States in Resonance Fluorescence

Philippe Campagne-Ibarcq, Landry Bretheau, Emmanuel Flurin +3 more

The fluorescence of a resonantly driven superconducting qubit is measured in the time domain, providing a weak probe of the qubit dynamics. Prior preparation and final, single-shot measurement of the qubit allows us to average fluorescence records conditionally on past and future knowledge. The resulting interferences reveal purely quantum features characteristic of weak values. We demonstrate conditional averages that go beyond classical boundaries and probe directly the jump operator associated with relaxation. The experimental results are remarkably captured by a recent theory, which generalizes quantum mechanics to open quantum systems whose past and future are known.The fluorescence of a resonantly driven superconducting qubit is measured in the time domain, providing a weak probe of the qubit dynamics. Prior preparation and final, single-shot measurement of the qubit allows us to average fluorescence records conditionally on past and future knowledge. The resulting interferences reveal purely quantum features characteristic of weak values. We demonstrate conditional averages that go beyond classical boundaries and probe directly the jump operator associated with relaxation. The experimental results are remarkably captured by a recent theory, which generalizes quantum mechanics to open quantum systems whose past and future are known.

arXiv:1311.5605Physical Review LettersMay 5, 201492 citations

Measuring the interferences between past and future quantum states in the resonant fluorescence of a superconducting qubit

Philippe Campagne-Ibarcq, Landry Bretheau, Emmanuel Flurin +3 more

When an atom or substance is irradiated, it can reemit some radiation by fluorescence, a process in which the transition from excited to ground state produces a photon. For a two-level system irradiated at resonance, the Rabi oscillations between ground and excited states leave a footprint in the resonant fluorescence. This can be seen in the fluorescence spectral density by the appearance of the so- called Mollow triplet, which is made of two side peaks around resonance. In a quantum information viewpoint, one may ask what information about the qubit is contained in the fluorescence. In order to answer this question optimally, one needs a system where both the qubit state and the fluorescence field can be measured in time. Superconducting qubits in cavity are fit for this task. We resonantly drove a superconducting qubit in a non-resonant cavity and measured the transmitted field as a function of time. Using the coupling between qubit and cavity it was also possible to measure whether the qubit was in ground or excited state at an arbitrary time. This experiment demonstrates how information about the qubit leaks out through fluorescence. In particular, the average values of the fluorescence measurement pre and post-selected on the qubit state exhibit non-classical weak values and perform a direct tomography of the non-hermitian field operator. This work provides a direct illustration of weak values in open systems which is perfectly explained by a recent theory.When an atom or substance is irradiated, it can reemit some radiation by fluorescence, a process in which the transition from excited to ground state produces a photon. For a two-level system irradiated at resonance, the Rabi oscillations between ground and excited states leave a footprint in the resonant fluorescence. This can be seen in the fluorescence spectral density by the appearance of the so- called Mollow triplet, which is made of two side peaks around resonance. In a quantum information viewpoint, one may ask what information about the qubit is contained in the fluorescence. In order to answer this question optimally, one needs a system where both the qubit state and the fluorescence field can be measured in time. Superconducting qubits in cavity are fit for this task. We resonantly drove a superconducting qubit in a non-resonant cavity and measured the transmitted field as a function of time. Using the coupling between qubit and cavity it was also possible to measure whether the qubit was in ground or excited state at an arbitrary time. This experiment demonstrates how information about the qubit leaks out through fluorescence. In particular, the average values of the fluorescence measurement pre and post-selected on the qubit state exhibit non-classical weak values and perform a direct tomography of the non-hermitian field operator. This work provides a direct illustration of weak values in open systems which is perfectly explained by a recent theory.

Dec 9, 20130 citations

Observing interferences between past and future quantum states in resonance fluorescence

Landry Bretheau, Philippe Campagne-Ibarcq, Emmanuel Flurin +3 more

Mar 3, 20141 citation

Observing Single Quantum Trajectories of a Superconducting Qubit

Irfan A. Siddiqi, Steven J. Weber, K. W. Murch +3 more

We monitor the quantum trajectory of a superconducting qubit as it evolves under a continuous weak measurement. We verify the trajectory using quantum state tomography and investigate statistical properties of ensembles of trajectories.

Research in Optical SciencesJan 1, 20145 citations

Resonance fluorescence readout of a superconducting qubit

Nathanaël Cottet, Yen‐Hsiang Lin, Long B. Nguyen +2 more

Bulletin of the American Physical SocietyMar 16, 20170 citations

Resonance fluorescence trajectories in superconducting qubit

Mahdi Naghiloo, Dian Tan, P. M. Harrington +3 more

Bulletin of the American Physical SocietyMar 14, 20170 citations

Observing interference between past and future quantum states in the resonance fluorescence

Abstract

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Observing interference between past and future quantum states in the resonance fluorescence

Abstract

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