Chiral ground-state currents of interacting photons in a synthetic magnetic field


The intriguing many-body phases of quantum matter arise from the interplay of particle interactions, spatial symmetries, and external fields. Generating these phases in an engineered system could provide deeper insight into their nature. Using superconducting qubits, we simultaneously realize synthetic magnetic fields and strong particle interactions, which are among the essential elements for studying quantum magnetism and fractional quantum Hall phenomena. The artificial magnetic fields are synthesized by sinusoidally modulating the qubit couplings. In a closed loop formed by the three qubits, we observe the directional circulation of photons, a signature of broken time-reversal symmetry. We demonstrate strong interactions through the creation of photon vacancies, or ‘holes’, which circulate in the opposite direction. The combination of these key elements results in chiral ground-state currents. Our work introduces an experimental platform for engineering quantum phases of strongly interacting photons.

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Figure 1: The unit cell for FQH and synthesizing magnetic fields.
Figure 2: Single-photon circulation resulting from the TRS breaking.
Figure 3: Signature of strong interaction.
Figure 4: Chiral currents in the ground state.


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We acknowledge discussions with L. Lamata, A. Rahmani, E. Rico, M. Sanz and E. Solano. Devices were made at the UCSB Nanofab Facility, part of the NSF-funded NNIN, and the NanoStructures Cleanroom Facility.

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P.R., C.N. and A.M. performed the experiment. E.K. provided theoretical assistance. P.R. analysed the data, and with C.N. and E.K. co-wrote the manuscript and Supplementary Information. All of the UCSB and Google team members contributed to the experimental set-up. All authors contributed to the manuscript preparation.

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Correspondence to P. Roushan.

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The authors declare no competing financial interests.

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Roushan, P., Neill, C., Megrant, A. et al. Chiral ground-state currents of interacting photons in a synthetic magnetic field. Nature Phys 13, 146–151 (2017).

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