We study the driven-dissipative dynamics of a network of spin-1/2 systems coupled to one or more chiral 1D bosonic waveguides within the framework of a Markovian master equation. We determine how the interplay between a coherent drive and collective decay processes can lead to the formation of pure multipartite entangled steady states. The key ingredient for the emergence of these many-body dark states is an asymmetric coupling of the spins to left and right propagating guided modes. Such systems are motived by experimental possibilities with internal states of atoms coupled to optical fibers, or motional states of trapped atoms coupled to a spin-orbit coupled BoseEinstein condensate. We discuss the characterization of the emerging multipartite entanglement in this system in terms of the Fisher information.

We consider the nonequilibrium dynamics of a driven dissipative spin chain with chiral coupling to a one-dimensional (1D) bosonic bath, and its atomic implementation with a two-species mixture of cold quantum gases. The reservoir is represented by a spin-orbit coupled 1D quasicondensate of atoms in a magnetized phase, while the spins are identified with motional states of a separate species of atoms in an optical lattice. The chirality of reservoir excitations allows the spins to couple differently to left-and right-moving modes, which in our atomic setup can be tuned from bidirectional to purely unidirectional. Remarkably, this leads to a pure steady state in which pairs of neighboring spins form dimers that decouple from the remainder of the chain. Our results also apply to current experiments with two-level emitters coupled to photonic waveguides.PACS numbers: 03.65. Yz, 67.85.Jk, 42.50.Dv, 03.67.Bg In an open quantum many-body system, the competition of particle interactions, external driving and the dissipative coupling to a quantum reservoir can result in novel scenarios for the formation of strongly correlated quantum states [1]. This is not only of interest as a nonequilibrium condensed matter problem per se [2-9], but dissipatively prepared entangled states also provide a potential resource for quantum information tasks [10][11][12][13][14][15]. Quantum optical systems of cold atoms or solid-state impurities provide a natural setting for such open manybody quantum systems. The paradigmatic example is given by an ensemble of two-level atoms driven by laser light, and coupled to a photonic reservoir [16][17][18][19], e.g., as one-dimensional (1D) engineered photonic band gap materials [20]. These model systems can be described as a collection of spin-1/2 systems, which via the photonic modes interact with long-range dipole-dipole interactions, and exhibit collective and enhanced decay into radiation modes of photonic structures. The realization of such Dicke-type models [21, 22] coupled to low-dimensional quantum reservoirs, and the observation of the associated dynamical quantum phases and phase transitions are, at present, an outstanding challenge in quantum optics [23][24][25][26].In the present work, we introduce a realization of dissipative quantum magnetism based on cold atoms in optical lattices [27,28], where the quantum reservoir is represented by phononic degrees of freedom of a 1D spin-orbit coupled Bose-Einstein quasicondensate (quasi-BEC) [29][30][31][32][33][34][35]. This model system provides a faithful and experimentally realistic representation of a chain of driven spin-1/2 particles coupled to a 1D bosonic bath. Crucially, spin-orbit coupling (SOC) makes the reservoir chiral, with the spins coupling differently to the left and right propagating modes, γ L = γ R [cf. Fig. 1(a)]. This asymmetry is, moreover, tunable via the atomic parameters, making it possible to engineer the spin-bath coupling from purely unidirectional to fully bidirectional.To describe the dynamics of our 1D spin c...

We propose to use the intrinsic two-level system (TLS) defect states found naturally in integrated optomechanical devices for exploring cavity QED-like phenomena with localized phonons. The Jaynes-Cummings-type interaction between TLS and mechanics can reach the strong coupling regime for existing nano-optomechanical systems, observable via clear signatures in the optomechanical output spectrum. These signatures persist even at finite temperature, and we derive an explicit expression for the temperature at which they vanish. Further, the ability to drive the defect with a microwave field allows for realization of phonon blockade, and the available controls are sufficient to deterministically prepare non-classical states of the mechanical resonator.Introduction.-Cavity optomechanics [1-3] has enabled the preparation of mechanical resonators in states of low phonon occupation via optomechanical (OM) sideband cooling [4][5][6][7][8][9], and to observe their quantum coherent interaction with light [9]. Further, OM systems have enabled displacement detection at or even below the standard quantum limit [10][11][12], thereby complementing other mechanics-based sensing applications [13,14]. They have also been proposed for creating macroscopic quantum superpositions [15] as well as for applications in quantum information [16,17]. However, in experiments carried out so far, the interaction between mechanical oscillator and cavity field is effectively linear, while one of the major challenges in the field is to realize non-linearities at the single phonon level. For example, the intrinsic OM radiation pressure non-linearity is predicted to enable the generation of non-classical states of light and mechanics [18,19], provided that the singlephoton coupling rate exceeds the mechanical frequency and the cavity decay rate. In multi-mode OM systems, the same non-linearity can be exploited more easily and it has been proposed to use it for enhanced readout [20] and quantum information processing [21].Here we propose an alternative route to render the dynamics of the mechanical oscillator nonlinear at the single quantum level: using its natural coupling to intrinsic structural two-level system (TLS) defects and thereby alleviating the need to functionalize the system [see Fig. 1(a)]. Ensembles of TLS defects were first studied in the context of the anomalous and universal low temperature properties of glasses [22][23][24][25][26], where they arise from frustration. In experiments involving Josephson junctions, individual TLSs with transition energies distributed well into the GHz regime were observed and studied for their role in decoherence [27]. Nevertheless, their comparatively long coherence times, and their ability to strongly couple to Josephson junctions via the electric dipole moment have enabled a TLS quantum memory [28]. In the same context, the influence of strain on TLSs has been probed recently [29]. However, in the OM setting, TLS ensembles have mainly been studied