Abstract
Microwave photons inside lattices of coupled resonators and superconducting qubits can exhibit surprising matterlike behavior. Realizing such open-system quantum simulators presents an experimental challenge and requires new tools and measurement techniques. Here, we introduce scanning defect microscopy as one such tool and illustrate its use in mapping the normal-mode structure of microwave photons inside a 49-site kagome lattice of coplanar waveguide resonators. Scanning is accomplished by moving a probe equipped with a sapphire tip across the lattice. This locally perturbs resonator frequencies and induces shifts of the lattice resonance frequencies, which we determine by measuring the transmission spectrum. From the magnitude of mode shifts, we can reconstruct photon field amplitudes at each lattice site and thus create spatial images of the photon-lattice normal modes.
- Received 4 December 2015
DOI:https://doi.org/10.1103/PhysRevX.6.021044
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Published by the American Physical Society
Viewpoint
A Bird’s Eye View of Circuit Photons
Published 30 June 2016
A scanning probe detects the quantum states of photons in a microwave circuit, providing the information needed for quantum simulations.
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Popular Summary
While measurements of global system properties are often readily obtained, measurements of more detailed local properties can provide a deeper understanding of the system at hand on a microscopic level. However, measuring local properties is often difficult. One solution is to use scanning probe measurements in which a probe is dragged across the surface of the system to create a local disturbance or defect. The effects of this defect can be tracked as a systematic change in a global measurement, allowing one to indirectly reconstruct an image of the local properties. Here, we introduce a new scanning probe tool that allows us to image the location of photons inside a lattice of microwave cavities.
We study a two-dimensional, 49-site lattice of superconducting microwave cavities that can serve as a backbone for realizing quantum phase transitions of light. The resonators in this cavity are connected via three-way capacitors. Our scanning probe consists of a sapphire dielectric roughly 2 mm on a side that we bring into close proximity with a lattice cavity, thereby shifting its frequency (by up to 663 MHz) and effectively “poking a hole” in the lattice; the transmission of photons through the lattice depends on the defect strength. By monitoring the changes in transmission of a coherent microwave tone while probing each cavity, we can image the amplitudes of electromagnetic normal modes on each lattice site. Once qubits are integrated into such lattices, mediated photon-photon interactions can give rise to emergent many-body states of light. We note that understanding such states through global measurements alone will be a tremendous challenge.
We expect that the local information accessed by our scanning probe will be useful for studying quantum phase transitions.