Nonreciprocal optical devices (NRODs) working in the quantum regime are the key building blocks for nonreciprocal quantum information processing. Conventional NRODs require a bias field, such as a strong control field or an external magnetic field, increasing the complexity in fabrication and operation. Here, we propose a bias-free nonmagnetic scheme for single-photon isolators and circulators on a solid-state platform. Our single-photon isolator is made of a chiral optical waveguide embedded with a negatively charged carbon nanotube quantum dot (CNQD), while the circulator with four ports consists of two optical waveguides and a whispering-gallery-mode optical microresonator coupling to a CNQD in a chiral way. The time-reversal symmetry in these two systems breaks because the inherent spin–orbit coupling of electrons and holes in the CNQD strongly lifts the energy degeneracies of two circularly polarized transitions. Under realistic experimental parameters, we obtain a low-loss and high-isolation-contrast single-photon isolator over a 10 gigahertz bandwidth and a circulator over a one gigahertz bandwidth, respectively, without requiring any bias (control) fields. Our bias-free design can greatly simplify the implementation and operation of NRODs and provide a compact solid-state platform for nonreciprocal quantum information processing.
Nonreciprocal optical devices (NRODs) working in the quantum regime are the key building blocks for nonreciprocal quantum information processing. Conventional NRODs require a bias field, such as a strong control field or an external magnetic field, increasing the complexity in fabrication and operation. Here, we propose a bias-free nonmagnetic scheme for single-photon isolators and circulators on a solid-state platform. Our single-photon isolator is made of a chiral optical waveguide embedded with a negatively charged carbon nanotube quantum dot (CNQD), while the circulator with four ports consists of two optical waveguides and a whispering-gallery-mode optical microresonator coupling to a CNQD in a chiral way. The time-reversal symmetry in these two systems breaks because the inherent spin–orbit coupling of electrons and holes in the CNQD strongly lifts the energy degeneracies of two circularly polarized transitions. Under realistic experimental parameters, we obtain a low-loss and high-isolation-contrast single-photon isolator over a 10 gigahertz bandwidth and a circulator over a one gigahertz bandwidth, respectively, without requiring any bias (control) fields. Our bias-free design can greatly simplify the implementation and operation of NRODs and provide a compact solid-state platform for nonreciprocal quantum information processing.
The nonreciprocal propagation of light at the single-photon level is essential for building a quantum network. Bulk optical schemes are lossy and difficulty to integrate onto a chip. We propose a single-photon optical diode and a three-port circulator without a magnetic field by coupling an unbalanced quantum impurity to a passive, linear optical waveguide or a whispering-gallery-mode microresonator which supports a locally or globally circularly polarized photon. Thanks to the unbalanced quantum Jaynes-Cummings coupling, the optical nonreciprocal propagation of single photons can be achieved without an external magnetic field. In particular, the three-port single-photon circulator can be accomplished using the existing experimental technology. The optical isolation can be reversed by selectively populating the initial state of the quantum impurity. Moreover, by using an ensemble of identical atoms filled in a hollow-core microbottle resonator, nonreciprocal propagation of weak light pulses can be achieved.
Nanophotonic components allow the control of the flow of light in integrated optical environments. Thereby, the light’s strong confinement leads to an inherent link between its local polarization and propagation direction which fundamentally alters the physics of light-matter interaction and gives rise to phenomena such as directional emission and direction-dependent coupling strengths [1]. I will present the underlying principles of this chiral light-matter interaction and its consequences for integrated applications [1]. In particular, I will show how we employ this effect to control the direction of spontaneous emission [2] and to realize low-loss nonreciprocal transmission at the single-photon level through a silica nanofiber [3]. We use two different approaches where either an ensemble of spin-polarized atoms is weakly coupled to a nanofiber or a single atom is strongly coupled to the nanofiber via a whispering-gallery-mode resonator. The resulting optical isolators show a strong imbalance between the transmissions in forward and reverse direction and, at the same time, a forward transmissions exceeding 70%. We extended this system to a 4-port device, where a single atom routes photons nonreciprocally from one fiber port to the next. This realizes a quantum optical circulator [4] which can even be prepared in a superposition of its operational modes. The demonstrated systems exemplify a new class of (quantum) nanophotonic devices that are ideally suited for photonic quantum information processing and quantum simulation. [1] Nature 541, 473, (2017). [2] Science 346, 67 (2014). [3] Phys. Rev. X 5, 041036 (2015). [4] Science 354, 1577 (2016).
On-chip single-photon nonreciprocal devices with high isolation and low insertion loss become a key element in quantum information processing. Based on electromagnetically induced transparency in chiral quantum systems, a single-photon isolator and a single-photon circulator are obtained without requiring unbalanced coupling. These devices have high isolation and low insertion loss. Moreover, their bandwidths are significantly broadened with the assistance of electromagnetically induced transparency.
Because the nonreciprocity has both theoretical and applicable prospects, it is desired to break through the restriction of the reciprocity principle for nonreciprocity optical transmission. Theoretically, the reciprocity principle is equivalent to the limited time reversal symmetry. To break the symmetry, the system should include nonlinearity, magneto-optical effects, or modulation in time. Some key components in the optical circuits, such as isolators, circulators, and phase shifters, are typical nonreciprocal devices. They are realized based on the Faraday effect of magneto-optical materials in traditional free-space optics. However, the magneto-optical materials are not naturally compatible with the integrated optics. Therefore, while pursuing the magneto-optical integration on a chip, people also devote to developing nonreciprocal theories and devices without magnetic materials. Whispering-gallery-modes (WGMs) optical microcavity has the advantages of small mode volume and high-quality factor. Therefore, many nonreciprocal strategies in photonic integration are based on optical microcavities. Similar to the nonreciprocal principle of the magneto-optical effect, the external bias fields (such as magnetic field, angular momentum, linear momentum, etc.) are necessary to break the time reversal symmetry. In this paper, we review the research on nonreciprocal optics in WGMs optical microcavities, and summarize recent research achievements in the following interaction categories: Magneto-optical effect, chiral coupling of atoms with energy level distribution bias, macroscopic Doppler effect with angular momentum bias, optomechanical driving, acousto-optic oscillation and nonlinear driving. Firstly, even on the chip, the magneto-optical effect is an important way to realize nonreciprocity. Nonreciprocity can be achieved by depositing/bonding magneto-optical materials on a silicon chip or using the spin-orbit interaction of WGMs in the YIG microsphere with the help of an external magnetic field. Secondly, preparing the atom to a specific Zeeman energy level can also lead to the polarization concerned interaction between the atoms and the photons, so that the nonreciprocity of the photon can be realized based on the control of the atomic ground state population. Thirdly, the Doppler effect can make the moving dielectric medium produce an additional refractive index related to the speed. Then the effective refractive index is different between the light propagating in the opposite directions. The reciprocity of the system is destroyed, thereby achieving nonreciprocity. Finally, the nonreciprocity of optomechanical systems, acousto-optic modulation, and nonlinear effects can be explained by the conservation of angular momentum of photon-phonon interactions. As a summary, some representative parameters of isolators obtained in related experiments are listed in the table. The existing solutions for nonreciprocity have also be classified in terms of angular momentum and interactions, which is beneficial to deeply understanding the existing solutions and to developing potential solutions. The research of nonreciprocity is also discussed by listing problems to be studied.
A fundamental obstacle to scalable solid-state quantum networks is the lack of a universal interface providing strong light-matter coupling, deterministic nonreciprocal photon routing, and efficient extraction. Here we propose a plasmonic platform overcoming these challenges using a Tomonaga-Luttinger liquid (TLL) in a single-walled carbon nanotube (SWCNT) microtoroid. The TLL's collective bosonic excitations are kinematically protected against backscattering by a large valley-momentum mismatch, guaranteeing robust chiral spin-momentum locking unattainable in dielectric cavities. This 1D protection enables deterministic routing of circularly polarized photons from a quantum emitter (e.g., a nitrogen-vacancy center) into distinct propagation channels. By aligning the emitter's symmetry axis, parasitic π transitions are geometrically forbidden. Furthermore, residual atomic-scale backscattering is suppressed to ~100 Hz via electrostatic gating and annealing. To overcome the severe mode mismatch between the CNT plasmon and optical fiber, we introduce a graded plasmonic-photonic mode converter, providing a path to near-unity extraction efficiency. Using a tripod-STIRAP scheme, we demonstrate high-fidelity, magnetically tunable spin-photon entanglement. Our analysis confirms operation deep in the strong-coupling regime, with cooperativities C > 100 and chiral contrast exceeding 20 dB. This wavelength-agnostic architecture is compatible with any solid-state emitter, establishing a scalable blueprint for robust, nonreciprocal quantum nodes in a global quantum internet.
Optical nonreciprocity has been a popular research topic in recent years. Semiconductor quantum wells (SQWs) play a key role in many high-performance optoelectronic devices. In this paper, we propose a theoretical scheme to achieve nonmagnetic optical nonreciprocity based on the four-wave mixing effect in SQW nanostructures. Using the experimentally available parameters, the nonreciprocal behavior of the probe field in forward direction and backward direction is achieved through this SQW, where both nonreciprocal transmission and nonreciprocal phase shift have high transmission rates. Furthermore, by embedding this SQW nanostructure into a Mach-Zender interferometer, a reconfigurable nonreciprocal device based on high transmission nonreciprocal phase shift that can be used as an isolator or a circulator, is designed and analyzed. The device can be realized as a two-port optical isolator with an isolation ratio of 92.39 dB and an insertion loss of 0.25 dB, and as a four-port optical circulator with a fidelity of 0.9993, a photon survival probability of 0.9518 and a low insertion loss with suitable parameters. Semiconductor media have the advantages of easier integration and tunable parameters, and this scheme can provide theoretical guidance for implementing nonreciprocal and nonreciprocal photonic devices based on semiconductor solid-state media.