Nonclassicality of multiphoton-added cat states

Remotely preparing Schrödinger cat states via non-Gaussian quantum steering in cascaded second-order spontaneous downconversion

Efficient generation of optical cat states using squeezed few-photon superposition states

Background and Aim: Topical nonsteroidal anti-inflammatory drugs are commonly used in feline ophthalmology, especially for long-term management of uveitis after cataract surgery. However, there is very limited data on how they affect the feline ocular surface, particularly the conjunctival tissue, goblet cell density (GCD), meibomian glands (MGs), and oxidative stress. This study assessed whether 15-day, thrice-daily application of 0.45% preservative-free ketorolac tromethamine (FKT) or 0.4% benzalkonium chloride (BAC)–preserved ketorolac tromethamine (BACKT) influences ocular surface disease scores, tear film parameters, GCD, MG morphology, matrix metalloproteinase-9 (MMP-9), and oxidative stress biomarkers (OSB) in healthy cats. Materials and Methods: A prospective, randomized, double-masked, crossover design was used with 13 healthy cats. Each cat received FKT in one eye and BACKT in the other eye every 8 h for 15 days, followed by a 3-week washout period and reversal of treatment. A separate control group (CG; n=13) received topical saline. Clinical assessments included conjunctival hyperemia, blepharospasm, Schirmer tear test (STT), tear film break-up time (TFBT), lissamine green, and fluorescein staining. Meibography was used to quantify MG loss. Conjunctival biopsies obtained at baseline and day 15 were analyzed for GCD, MMP-9, superoxide dismutase, catalase, reduced glutathione, and malondialdehyde levels. Results: No groups showed corneoconjunctival staining or conjunctival hyperemia at any point. Mild blepharospasm developed in 3 out of 13 FKT-treated eyes and 9 out of 13 BACKT-treated eyes (p = 0.003). STT values significantly decreased from baseline to day 15 in both FKT and BACKT groups (p < 0.05). TFBT decreased significantly only in FKT-treated eyes (p = 0.009), although BACKT showed a similar, non-significant trend. MG loss increased significantly only in BACKT-treated eyes (p = 0.04). GCD decreased markedly in both FKT (p = 0.0003) and BACKT (p < 0.0001) groups and was lower than CG at day 15. OSB remained largely unchanged, except for higher MDA levels in BACKT-treated eyes compared with CG (p = 0.04). MMP-9 expression did not differ within or between groups. Conclusion: Both ketorolac formulations reduced STT, TFBT, and GCD, supporting the development of a qualitative dry eye state in healthy cats. BACKT resulted in greater ocular discomfort, increased MG loss, and higher lipid peroxidation, indicating BAC-related cytotoxicity. Caution is advised when prescribing prolonged topical ketorolac, and concurrent ocular lubrication is recommended. Keywords: benzalkonium chloride, feline ophthalmology, goblet cell density, Ketorolac tromethamine, matrix metalloproteinase-9, meibomian gland loss, ocular surface disease, oxidative stress biomarkers, Schirmer tear test, tear film break-up time.

This study advances economical Quantum Teleportation (QT) schemes for cat states across arbitrary dimensional Hilbert spaces. First, we develop a protocol for teleporting an unknown two-dimensional cat state using a three-dimensional maximally entangled three-qutrit quantum channel. The approach involves constructing a complete orthogonal nonsymmetric measurement basis, where the sender performs joint measurements on three particles. The receiver then applies dimension-specific unitary operations conditioned on measurement outcomes to reconstruct the target state. Subsequently, we extend this protocol by replacing the maximally entangled channel with a nonmaximally entangled three-qutrit state. Through auxiliary qubit introduction and optimized operations, the two-qubit cat state is probabilistically recovered. We derive the success probability for both protocols, demonstrating that the nonmaximally entangled case generalizes the former scheme. Further generalization is achieved through two nonsymmetric basis constructions: (i) Scaling quantum channel dimension from 3 to [Formula: see text] dimensions; (ii) Extending transmitted cat states from 2 to [Formula: see text] dimensions [Formula: see text]. These dual-dimensional generalizations establish distinct economical advantages over existing QT schemes.

Reservoir-engineered mechanical cat states with a driven qubit

Decoherence of Schrödinger cat states in light of wave/particle duality

We investigate the striking properties that magnetoresistance of irradiated two-dimensional electron systems presents when their mobility is ultra-high ([Formula: see text]) and temperature is low ([Formula: see text] K). Such as, an abrupt magnetoresistance collapse at low magnetic field and a resonance peak shift to the second harmonic ([Formula: see text]), [Formula: see text] and w being the cyclotron and radiation frequencies, respectively. We appeal to the principle of quantum superposition of coherent states and find that Schrödinger cat states (even and odd) are key to explaining magnetoresistance at these extreme mobilities. On the one hand, the Schödinger cat state system oscillates as a whole with [Formula: see text]. Then, it would resonate with radiation at [Formula: see text], thus being responsible for the shift of the resonance peak at the second harmonic. On the other hand, we find that Schrödinger cat states-based scattering processes give rise to a destructive effect when the odd states are involved, leading to a magnetoresistance collapse. The Aharonov-Bohm effect plays a central role in the latter, turning even cat states into odd ones. We show that ultra-high mobility two-dimensional electron systems could make a promising bosonic mode-based platform for quantum computing.

Creation and manipulation of Schrödinger cat states based on semiclassical predictions

We suggest a new technique for bidirectional quantum teleportation (BQT) that combines coherent-state encoding with discrete-time quantum walks to allow two users to communicate quantum information simultaneously. Our method enables Alice and Bob to simultaneously teleport quantum states to one another within a single protocol, as compared to unidirectional teleportation, which only transmits quantum states in one direction. To allow for a qubit-like representation and fidelity analysis using Bloch vector formalism, the quantum information is encoded using non-orthogonal coherent states that are converted into an orthonormal basis of even and odd Schrödinger cat states. Four different quantum walk steps, each acting on a three-part quantum system made up of position and coin spaces, drive the teleportation process. We use density matrix overlaps in the even–odd basis to derive closed-form formulas for teleportation fidelity in both directions analytically. Using the SeQUeNCe discrete-event simulator, we simulate large-scale quantum network settings with realistic limitations, including photon loss, memory decoherence, entanglement swapping degradation, and various channel capacities in order to evaluate the potential of our approach. We evaluate quantum memory utilization, throughput, and end-to-end fidelity in various network topologies and scenarios. Our findings demonstrate that BQT allows symmetric communication with strong fidelity, particularly in high-capacity and large-scale network situations, but requires a greater resource overhead than unidirectional protocols. The hybrid framework developed in this study offers a scalable and analytically simple solution for next-generation quantum communication systems by combining discrete-time quantum evolution with continuous-variable state encoding.

We propose and numerically validate a scheme for the realization of Schrödinger cat-like states in a two-component Bose-Einstein condensate, emphasizing their twinning across components under tunable intra- and inter-species interactions within the miscibility regime. Wigner phase-space analysis reveals sub-Planck-scale interference fringes, confirming the nonclassical character of the states and their potential utility in quantum-enhanced metrology. The dynamical response of the system to a weak linear gravitational-like perturbation further demonstrates cooperative enhancement: while the directly perturbed component retains its cat-like features, the coupled partner exhibits a pronounced population imbalance and a distinct phase-space rotation, providing a sensitive detection channel absent in single-component condensates. These results establish binary condensates as a versatile platform for engineering macroscopic quantum superpositions and exploiting their twinning dynamics for precision measurements.

We explore the non-classicality and precision limits of coherent superposition mechanical states generated in a Mach-Zehnder interferometer (MZI). In this setup, a photonic NOON state interacts with a mechanical oscillator, producing such coherent superposition states that give rise to Schrödinger cat (SC) states at specific times and phase differences. The non-classicality is quantified via the negativity volume (NV) of the Wigner function, and the precision limit of the mechanical state is characterized by the quantum Fisher information (QFI). We observe that NV and QFI exhibit correlated trends at selected times and phase differences, indicating that higher non-classicality may enhance the precision limits. Notably, for certain instances, QFI can remain high even when fidelity between the coherent superposition state and the target SC state is low, indicating that conditional states can encode substantial phase information. Using parity detection, we demonstrate that the quantum Cramér-Rao bound (CRB) can be saturated, reaching the Heisenberg limit (HL) for certain evolution times and confirming it as the optimal detection strategy. These results provide insights into the quantum dynamics of optomechanical systems for high-precision measurements and enable the creation of high-fidelity SC states.

Generation of generalized two-mode Schrödinger cat state through strong ground-state coupling

Cat states carrying long-range correlations in the many-body localized phase

Optimizing decoherence in the generation of optical Schrödinger cat states

Quantum metrology enables sensitivity to approach the limits set by fundamental physical laws. Even a single continuous mode offers enhanced precision, with the improvement scaling with its occupation number. Due to their high information capacity, continuous modes allow for the engineering of quantum non-Gaussian states, which not only improve metrological performance but can also be tailored to specific experimental platforms and conditions. Recent advancements in control over continuous platforms operating in the quantum regime have renewed interest in sensing weak forces, also coupling to massive macroscopic objects. In this work, we investigate a force-sensing scheme where a physical process completely randomizes the direction of the induced phase-space displacement, and the unknown force strength is inferred through excitation-number-resolving measurements. We find that N-spaced states, where only every N^{th} Fock state occupation is nonzero, approach the achievable sensing bound. Additionally, non-Gaussian states are shown to be more resilient against decoherence than their Gaussian counterparts with the same occupation number. While Fock states typically offer the best protection against decoherence, we uncover a transition in the metrological landscape-revealed through a tailored decoherence-aware Fisher-information-based reward functional-where experimental constraints favor a family of number-squeezed Schrödinger cat states. Specifically, by implementing quantum optimal control in a minimal spin-boson system, we identify these states as maximizing force sensitivity under lossy dynamics and finite system controllability. Our results provide a pathway for enhancing force sensing in a variety of continuous quantum systems, ranging from massive systems like mechanical oscillators to massless systems such as quantum light and microwave resonators.

Quantum state tomography typically requires exponentially many copies of a quantum state, due to the complex correlations present in large systems. We show that, for bosonic systems, the scaling is completely determined by the nature of these correlations. Motivated by the Hong-Ou-Mandel effect and boson sampling, we define Gaussian-entanglable (GE) states, produced by generalized interference between separable bosonic modes. GE states greatly extend the Gaussian family, encompassing separable states, multi-mode Gottesman-Kitaev-Preskill codes, entangled cat states, and boson-sampling outputs—resources for error correction and quantum advantage. We prove that any pure GE state of m modes can be learned efficiently, requiring only poly(m) copies, via a protocol based on Gaussian unitaries, local tomography, and classical post-processing; for boson-sampling states, no Gaussian unitaries are needed. For states outside GE, we define an operational monotone—the minimal number of ancillary modes needed to make them GE—which exactly characterizes the exponential tomography overhead. We also show that deterministic generation of NOON states with N ≥ 3 via two-mode interference is impossible.

We investigate the effect of giant negative magnetoresistance in ultrahigh-mobility (μ≫107cm2V−1s−1) two-dimensional electron systems. These systems present a dramatic drop in the mangetoresistance at low magnetic fields (B∼0.1 T) and temperatures (T∼0.1 K). This effect is reversed by increasing the temperature or the presence of an in-plane magnetic field. The motivation for the present work is to develop a microscopical model to explain the experimental evidence, based on coherent states and Schródinger cat states of the quantum harmonic oscillator. Thus, we approach the giant negative magnetoresistance effect based on the description of ultrahigh-mobility two-dimensional electron systems in terms of Schrödinger cat states (superposition of coherent states of the quantum harmonic oscillator). We explain the experimental results in terms of the increasing disorder in the sample due to the rising temperature or the in-plane magnetic field, breaking up the Schrödinger cat states and giving rise to mere coherent states, which hold magnetoresistance in lower-mobility samples. The latter, jointly with the description of ultrahigh-mobility samples with Schrödinger cat states, accounts for the main contribution. The most interesting application of this novel description of such systems would be in the implementation of qubits for quantum computing based on bosonic models.

We propose a novel method to generate a rotational Schrödinger’s cat state made of a superposition of coherent angular oscillations (librations) of a levitated magnonic nanoparticle. By taking advantage of the magnetocrystalline anisotropy, we achieve quadratic magnon-rotational coupling. This coupling is particularly significant for small nanoscale objects. By driving the magnon with a bichromatic microwave field, we induce nonlinear rotational dissipation and parametrically excite the libration motion. This enables an efficient generation of a rotational cat state, which, under high vacuum conditions, can persist for several minutes. Our approach provides a robust and novel platform for exploring quantum superposition of rotation, which has potential applications in testing collapse models and gravitational effects on rotating quantum objects.

The Dicke-Ising model, one of the few paradigmatic models of matter-light interaction, exhibits a superradiant quantum phase transition above a critical coupling strength. However, in natural optical systems, its experimental validation is hindered by a “no-go theorem.” Here, we propose a digital-analog quantum simulator for this model based on an ensemble of interacting qubits coupled to a single-mode photonic resonator. We analyze the system's free-energy landscape using field-theoretical methods and develop a digital-analog quantum algorithm that disentangles qubit and photon degrees of freedom through a parity-measurement protocol. This disentangling enables the emulation of a photonic Schrödinger cat state, which is a hallmark of the superradiant ground state in finite-size systems and can be unambiguously probed through the Wigner tomography of the resonator's field.