We propose how to create and manipulate one-way nonclassical light via photon blockade in rotating nonlinear devices. We refer to this effect as nonreciprocal photon blockade (PB). Specifically, we show that in a spinning Kerr resonator, PB happens when the resonator is driven in one direction but not the other. This occurs because of the Fizeau drag, leading to a full split of the resonance frequencies of the countercirculating modes. Different types of purely quantum correlations, such as single-and two-photon blockades, can emerge in different directions in a wellcontrolled manner, and the transition from PB to photon-induced tunneling is revealed as well. Our work opens up a new route to achieve quantum nonreciprocal devices, which are crucial elements in chiral quantum technologies or topological photonics.

Coupling between superradiant and subradiant mode resonators in a metamaterial unit cell plays an important role in observing the sharp transparency peak due to destructive interference between the resonators. This effect is enhanced as the resonators are brought closer to each other in a conventional planar arrangement. We present a novel coupling scheme of planar terahertz metamaterial to tune the plasmon-induced transparency peak by physically varying the distance between the superradiant and the subradiant resonators in such a way that the transparency peak begins to disappear as the coupled resonators are brought closer than a critical separation distance. The effect is attributed to the disappearance of the resonant behavior of the subradiant resonator in a closely coupled regime. The simple planar design presented here demonstrates a scheme to manipulate the electromagnetically induced transparency-like behavior in terahertz metamaterials and this could lead to the development of unique slow light devices for terahertz applications.

We propose how to achieve quantum nonreciprocity via unconventional photon blockade (UPB) in a compound device consisting of an optical harmonic resonator and a spinning optomechanical resonator. We show that, even with a very weak single-photon nonlinearity, nonreciprocal UPB can emerge in this system, i.e., strong photon antibunching can emerge only by driving the device from one side, but not from the other side. This nonreciprocity results from the Fizeau drag, leading to different splitting of the resonance frequencies for the optical counter-circulating modes. Such quantum nonreciprocal devices can be particularly useful in achieving back-action-free quantum sensing or chiral photonic communications. * miran@amu.edu.pl † jinghui73@gmail.com light, which is optimally sub-Poissonian in second order, g 2 (0) ≈ 0, and is generated in a weakly-nonlinear system allowing for multi-path interference (e.g., two linearlycoupled cavities, when one of them is also weakly coupled to a two-level atom). Thus, PB and UPB are induced by different effects: PB due to a large system nonlinearity and UPB via multi-path interference assuming even an extremely-weak system nonlinearity. Note that light generated via UPB can exhibit higher-order super-Poissonian photon-number statistics, g (n) (0) > 1 for some n > 2. Thus, UPB is, in general, not a good source of single photons. This short comparison of PB and UPB indicates that the term UPB, as coined in Ref.[39] and now commonly accepted, is fundamentally different from PB, concerning their physical mechanisms and properties of their generated light.Here, we propose to achieve and control nonreciprocal UPB with spinning devices. Nonreciprocal devices allow for the flow of light from one side but block it from the other. Thus, such devices can be applied in noisefree quantum information signal processing and quantum communication for cancelling interfering signals [40]. Nonreciprocal optical devices have been realized in OM devices [40][41][42], Kerr resonators [43][44][45], thermo systems [46][47][48], devices with temporal modulation [49,50], and non-Hermitian systems [51][52][53]. In a very recent experiment [54], 99.6% optical isolation in a spinning resonator has been achieved based on the optical Sagnac effect. However, these studies have mainly focused on the classical regimes; that is, unidirectional control of transmission rates instead of quantum noises. We also note that in recent works, single-photon diodes [55][56][57], unidirectional quantum amplifiers [58][59][60][61][62], and one-way quantum routers [63] have been explored. In particular, nonreciprocal PB was predicted in a Kerr resonator [64] or a quadratic OM system [65], which, however, relies on the conventional condition of strong single-photon nonlinearity. These quantum nonreciprocal devices have potential applications for quantum control of light in chiral and topological quantum technologies [66].

Non-Hermitian systems, with symmetric or antisymmetric Hamiltonians under the parity-time (PT) operations, can have entirely real or imaginary eigenvalues. This fact has led to surprising discoveries such as loss-induced lasing and topological energy transfer. A merit of anti-PT systems is free of gain, but in recent efforts on making anti-PT devices, nonlinearity is still required. Here, counterintuitively, we show how to achieve anti-PT symmetry and its spontaneous breaking in a linear device by spinning a lossy resonator. Compared with a Hermitian spinning device, significantly enhanced optical isolation and ultrasensitive nanoparticle sensing are achievable in the anti-PT-broken phase. In a broader view, our work provides a new tool to study anti-PT physics, with such a wide range of applications as anti-PT lasers, anti-PT gyroscopes, and anti-PT topological photonics or optomechanics.

We investigate the effect of tweaking the quality (Q) factor of split ring resonators in a coupled state, giving rise to plasmonic induced transparency (PIT) which has two distinct, individually engineered resonance modes. The Q factor and the amplitude of each resonance are tuned by twisting them mutually in the unit cell consisting of a subradiant and a superradiant resonator. We experimentally observe that introducing a gradual twist in the three U-shape resonators has a dramatic impact on the PIT spectral response, leading to the disappearance of the transparency peak beyond a certain critical degree of twist. This mainly happens due to the change in the in-plane coupling between the resonators as well the variation in coupling of the twisted resonators with the incident electric field. Further investigation based on the Fano model provides good agreement with the experimental results. The scheme presented here for controlling the Q factor of each resonator in the coupled regime is a unique way to tune the PIT response in terahertz metamaterials and can be easily scaled across the entire electromagnetic spectrum.