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Quantum optical circulator controlled by a single chirally coupled atom
Michael Scheucher, Adèle Hilico, Elisa Will, Jürgen Volz, Arno Rauschenbeutel
TL;DR
The paper investigates fiber-integrated circulator operation using a single atom and characterizes its transmission through measurements and modeling. It reports atom-state-dependent routing, an optimal normalized coupling point of κtot/2κ0 = 2.2, and photon-correlation signatures of quantum nonlinearity, while identifying experimental constraints on direct transmission measurement and some routing paths.
Problem
Direct measurement of the circulator transmissions is not possible because of the a priori ...
Method
The experiment uses an atomic fountain, optical pumping into selected Zeeman states, transmission measurements, and a theoretical model of atom–resonator coupling.
Results
κtot/2κ0 = 2.2 is the optimal working point, where the relevant transmissions are explicitly listed and the modeled transmission curves describe the measurements.
Takeaways & Limitations
The circulator’s photon survival probability is independent of polarization under the modeled equal-coupling condition κa = κb = κ.
Takeaways & Limitations
Direct transmission measurement is not possible, and 2 →3 and 4 →1 performance is affected by optical pumping effects.
Abstract
from arXiv · showhide
We demonstrate a fiber-integrated quantum optical circulator that is operated by a single atom and that relies on the chiral interaction between emitters and transversally confined light. Like its counterparts in classical optics, our circulator exhibits an inherent asymmetry between light propagation in the forward and the backward direction. However, rather than a magnetic field or a temporal modulation, it is the internal quantum state of the atom that controls the operation direction of the circulator. This working principle is compatible with preparing the circulator in a coherent superposition of its operational states. Such a quantum circulator may thus become a key element for routing and processing quantum information in scalable integrated optical circuits. Moreover, it features a strongly nonlinear response at the single-photon level, thereby enabling, e.g., photon number-dependent routing and novel quantum simulation protocols.
Competing Interests
The authors declare that they have no competing financial interests.
- The authors report no competing financial interests.
Correspondence
The paper presents a single-atom, fiber-integrated circulator whose direction is controlled by atom–light coupling and whose routing is characterized through transmission and photon-correlation measurements.
- A single rubidium 85 atom couples to a bottle-resonator whispering-gallery mode interfaced by two tapered fiber couplers.
- The atom’s Zeeman state selects the stronger coupling direction because evanescent-field polarization depends on clockwise or counterclockwise propagation.
- For mF = +3, light is routed sequentially from port 1 to 2, 2 to 3, 3 to 4, and 4 to 1.
- Transmission, operation fidelity, and photon survival probability are measured versus normalized resonator decay rate and compared with a theoretical model.
- The transmission matrices show nonreciprocal routing with mF = +3, reversed operation with mF = −3, and reciprocal behavior without the atom.
- The circulator exhibits antibunching for 1 →2 and 3 →4 and bunching for 1 →4 and 3 →2 in second-order photon correlations.
Materials and Methods
The experiment uses a fiber-integrated resonator system with a single 85Rb atom, real-time state preparation, and transmission measurements across all input–output configurations. The circulator is modeled with direction-dependent atom–resonator coupling, while measurements account for auxiliary-network losses and finite coupling effects.
- Experimental procedure: A laser-cooled 85Rb atom is delivered to the resonator, and its presence is detected through a two-orders-of-magnitude increase in transmission through fiber a.Detection light resonant with the empty resonator and the 85Rb D2 transition optically pumps the atom into |F = 3, mF = +3⟩.
- Experimental procedure: Real-time control switches from detection to probe light within approximately 150 ns after the transmission increase.The probe field is sent for 400 ns, followed by a 1 µs re-detection interval to verify continued atom–resonator coupling.
- Experimental procedure: The probe sequence is repeated for input ports i ∈ {1, 2, 3, 4}, with the input port incremented consecutively during each full experimental cycle.The probe photon fluxes for the four inputs are (8, 6, 11, 6) photons/µs.
- Transmission measurements: Direct transmission measurement is prevented by unknown auxiliary-network input and output losses and unknown detector efficiencies.The experiment therefore derives transmissions using normalization measurements and the modeled empty-resonator response.
- Modeling the circulator transmission: The circulator model decomposes the atomic V-type system into two independent two-level systems with direction-dependent couplings gcw and gccw.The resulting forward and backward operation is described by a Jaynes–Cummings Hamiltonian and a Lindblad superoperator with total decay rate κtot = κ0 + κa + κb.