Chiral route to spontaneous entanglement generation

Abstract

We study the spontaneous entanglement generation between two qubits chirally coupled to a waveguide. The maximum achievable concurrence is demonstrated to increase by a factor of 4/e ∼ 1.5 as compared to the nonchiral coupling situation. The proposed entanglement scheme is shown to be robust against variation of the qubit properties such as detuning and separation, which are critical in the nonchiral case. This result relaxes the restrictive requirements of the nonchiral situation, paving the way toward a realistic implementation. Our results demonstrate the potential of chiral waveguides for quantum entanglement protocols.

Chiral quantum optics

“…This can be achieved by combining Λ-type three level systems with the two ground states representing the qubit and a Raman process involving a chiral coupling [67]. The advantage of having chiral coupling for the generation of emitter-emitter entanglement and the robustness towards imperfections has been recently studied [67,68]. The directional photon exchange between emitters with chiral interactions offers interesting novel perspective for many-body quantum dynamics.…”

Multiqubit entanglement in bidirectional-chiral-waveguide QED

“…The quantity Γ i is the emission rate of the ith atom into the free space channel; such decays are ignored in the present analysis. Consequently, the coupling fraction parameter [14] …”

“…Some appealing examples in this regard are: plasmonic waveguides [8], photonic crystals [9,10], superconducting circuits [11] and optical lattices [12]. In previous waveguide QED studies, two qubit entanglement generation has been analyzed when either an input coherent field or a single photon (produced through an excited qubit) serve as a qubitqubit entanglement agent [13][14][15]. However, an actual quantum network will in general require multiple qubits, wherein flying photons will serve as information carriers.…”

“…We focus specifically on the question of how system parameters can be engineered to control waveguide mediated qubit-qubit entanglement. As opposed to choosing a fixed atom as a single photon source [14], here we consider the situation in which a single photon Gaussian wavepacket serves both as an input drive and an entanglement generator. To this end, we derive and then utilize a single-photon bi-directional Fock state master equation.…”

“…The three main approaches used in waveguide QED to study scattering of photons and entanglement are: the real space formalism [18], the input-output formalism [19,20] and other master equation approaches [14,21]. The main novelty of using the Fock state master equation relies on the fact that it captures both the qubit dynamics and keeps track of the state of the reservoirs at the same time, due to its non-markovian structure.…”