Microwave-Controlled Generation of Shaped Single Photons in Circuit Quantum Electrodynamics

Abstract

Large-scale quantum information processors or quantum communication networks will require reliable exchange of information between spatially separated nodes. The links connecting these nodes can be established using traveling photons that need to be absorbed at the receiving node with high efficiency. This is achievable by shaping the temporal profile of the photons and absorbing them at the receiver by time reversing the emission process. Here, we demonstrate a scheme for creating shaped microwave photons using a superconducting transmon-type three-level system coupled to a transmission line resonator. In a second-order process induced by a modulated microwave drive, we controllably transfer a single excitation from the third level of the transmon to the resonator and shape the emitted photon. We reconstruct the density matrices of the created single-photon states and show that the photons are antibunched. We also create multipeaked photons with a controlled amplitude and phase. In contrast to similar existing schemes, the one we present here is based solely on microwave drives, enabling operation with fixed frequency transmons.

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Plain Language Summary

Today’s communication networks span the entire globe and allow us to share and process information on a worldwide scale. Networks based on the principles of quantum mechanics have the potential to enable novel ways of exchanging and processing information, for example, by providing intrinsically secure communication channels or using computers harnessing the inherent parallelism of quantum information processing. Such quantum networks will likely consist of spatially separated nodes with quantum bits (qubits) exchanging information by emitting and absorbing photons. While photons are natural candidates for mobile quantum information carriers because of their weak interactions with the environment, interfacing photons with stationary qubits in an efficient way requires care. One method of engineering this interface is to change the emission of a photon to make its waveform symmetric in time. Then, this process can be reversed at the receiving qubit to absorb the photon with high efficiency.

We demonstrate the controlled emission of a microwave photon from an artificial atom realized by a superconducting circuit on a chip—an engineered quantum system known for its strong coupling between qubits and microwave photons. We shape the waveform of the photon by irradiating the atom with a tunable microwave pulse that triggers the release of the photon and regulates its amplitude and phase. We use this method to generate photon shapes symmetric in time. We are also able to create single-photon pulses with multiple peaks, where the phase of each peak can be controlled independently.

With precise control over the photon emission process, our experiment realizes an important step toward coherent quantum networks based on a scalable solid-state system. We expect that our results may be useful for quantum circuits based on three-dimensional cavities.