Single-atom laser generates nonlinear coherent states

The stationary state of a single-atom (single-qubit) laser is shown to be a phase-averaged nonlinear coherent state - an eigenstate of a specific deformed annihilation operator. The solution found for the stationary state is unique and valid for all regimes of the single-qubit laser operation. We have found the parametrization of the deformed annihilation operator which provides superconvergence in finding the stationary state by iteration. It is also shown that, contrary to the case of the usual laser with constant Einstein coefficients describing transition probabilities, for the single-atom laser the interaction-induced transition probabilities effectively depend on the field intensity

Weak Cross-Kerr Nonlinearity as a Resource for Quantum State Engineering.

Quantum information processing and creation of nonclassical and nonlocal quantum states require presence of a nonlinear element, being challenging to construct and representing a physical resource that should be used in an optimal way. We propose a protocol exploiting only weak cross-Kerr nonlinearities for generating a wide class of continuous variables states of optical systems separated by distances up to more than 100 km. The equation, derived in our work, shows that the protocol parameters are defined in a unique way by the desired final state

Nonlinear Coherent Loss

We discuss exploiting artificially designed nonlinear coherent loss for generating non-classical states of a bosonic mode. Of special interest is the case when superpositions of Fock states are generated. We discuss conditions necessary for generation of pure superpositions and estimate maximal achievable fidelity. It is shown that the fidelity can be arbitrary close to unity for generation of either single Fock state, or infinite superposition of equidistant Fock states (e.g. a superposition of Fock states with odd number of particles), but is limited by the value 0.94, for instance, for superpositions of any two Fock states. Certain general necessary and (or) sufficient conditions for generation of pure states are also provided and illustrated by examples

Nonlinear Coherent Loss

We discuss exploiting artificially designed nonlinear coherent loss for generating non-classical states of a bosonic mode. Of special interest is the case when superpositions of Fock states are generated. We discuss conditions necessary for generation of pure superpositions and estimate maximal achievable fidelity. It is shown that the fidelity can be arbitrary close to unity for generation of either single Fock state, or infinite superposition of equidistant Fock states (e.g. a superposition of Fock states with odd number of particles), but is limited by the value 0.94, for instance, for superpositions of any two Fock states. Certain general necessary and (or) sufficient conditions for generation of pure states are also provided and illustrated by examples

Efficiently reconstructing compound objects by quantum imaging with higher-order correlation functions

Quantum imaging has a potential of enhancing the precision of objects reconstruction by exploiting quantum correlations of the imaging field, in particular for imaging with low-intensity fields up to the level of a few photons. However, it generally leads to nonlinear estimation problems. The complexity of these problems rapidly increases with the number of parameters describing the object and the correlation order. Here we propose a way to drastically reduce the complexity for a wide class of problems. The key point of our approach is to connect the features of the Fisher information with the parametric locality of the problem, and to reconstruct the whole set of parameters stepwise by an efficient iterative inference scheme that is linear on the total number of parameters. This general inference procedure is experimentally applied to quantum near-field imaging with higher-order correlated light sources, resulting in super-resolving reconstruction of grey compound transmission objects