Quadruplets of exceptional points and bound states in the continuum in dielectric rings

In photonics, most systems are non-Hermitian due to radiation into open space and material losses. At the same time, non-Hermitianity defines a new physics, in particular, it gives rise to a new class of degenerations called exceptional points, where two or more resonances coalesce in both eigenvalues and eigenfunctions. The point of coalescence is a square root singularity of the energy spectrum as a function of interaction parameter. We investigated analytically and numerically the photonic properties of a narrow dielectric resonator with a rectangular cross section. It is shown that the exceptional points in such a resonator exist in pairs, and each of the points is adjacent in the parametric space to a bound state in the continuum, as a result of which quadruples of singular photonic states are formed. We also showed that the field distribution in the cross section of the ring is a characteristic fingerprint of both the bound state in the continuum and the exceptional point.Comment: 12 pages, 5 figure

Topologically protected entanglement switching around exceptional points

The robust operation of quantum entanglement states are crucial for applications in quantum information, computing, and communications1-3. However, it has always been a great challenge to complete such a task because of decoherence and disorder. Here, we propose theoretically and demonstrate experimentally an effective scheme to realize robust operation of quantum entanglement states by designing quadruple degeneracy exceptional points. By encircling the exceptional points on two overlapping Riemann energy surfaces, we have realized a chiral switch for entangled states with high fidelity. Owing to the topological protection conferred by the Riemann surface structure, this switching of chirality exhibits strong robustness against perturbations in the encircling path. Furthermore, we have experimentally validated such a scheme on a quantum walk platform. Our work opens up a new way for the application of non-Hermitian physics in the field of quantum information

Demonstration of fully integrated parity-time-symmetric electronics

Harnessing parity-time (PT) symmetry with balanced gain and loss profiles has created a variety of opportunities in electronics from wireless energy transfer to telemetry sensing and topological defect engineering. However, existing implementations often employ ad-hoc approaches at low operating frequencies and are unable to accommodate large-scale integration. Here, we report a fully integrated realization of PT-symmetry in a standard complementary metal-oxide-semiconductor technology. Our work demonstrates salient PT-symmetry features such as phase transition as well as the ability to manipulate broadband microwave generation and propagation beyond the limitations encountered by exiting schemes. The system shows 2.1 times bandwidth and 30 percentage noise reduction compared to conventional microwave generation in oscillatory mode and displays large non-reciprocal microwave transport from 2.75 to 3.10 gigahertz in non-oscillatory mode due to enhanced nonlinearities. This approach could enrich integrated circuit (IC) design methodology beyond well-established performance limits and enable the use of scalable IC technology to study topological effects in high-dimensional non-Hermitian systems.Comment: 52 pages (16 pages Main Text, 28 pages Supplementary Materials, 4 pages reference), 27 figures (4 figures Main Text, 23 figures Supplementary Materials), 93 references (50 references Main Text, 43 references Supplementary Materials

Cavity Mediated Spin-1 Atom Interaction

In this thesis a theoretical framework for a spin-1 exchange dynamics is developed by the use of effective Hamiltonian theory. We develop this framework through several applications beginning with the standard Jaynes-Cummings model, which under the method of time-averaging leads to the Hamiltonian described by one-axis twisting in a more efficient manner than standard adiabatic elimination. The process of developing effective many-body spin Hamiltonian’s is then applied in several contexts. The robustness of the systems we studied are demonstrated through the generation of entangled states under various constraints. We find that when fixed within a sub-manifold of the collective angular momentum states the time evolution of minimally uncertain atomic states results in atomic cat states, which have been utilized in a variety of contexts for precision measurements. More so, when the initial state is given freedom to evolve between all angular momentum sub-manifolds large degrees of entanglement results. We give analytic results for the case of two-atoms where the entanglement quantification is given through the fidelity, and Schmidt number. This gives implications for measurement protocols through Ramsey pulses, quantum simulators, and creation of spin-1 Bell states for teleportation. Under different operating conditions, we demonstrate the emergence of electromagnetically induced transparency(EIT) which provides a platform for quantum memory, polarization conversion, and state transfer. A limitation of photonic processes is the short optical resonance lifetime, however, our system is free of this issue due to the dispersive approximation constraining the system to a decoherence free ground state manifold. As a result our EIT scheme can result in longer storage times, and more efficient state transfer as decoherence due to spontaneous emission is not the limiting factor