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arXiv:2007.09111 · Physical Review A

Dynamical blockade in a bosonic Josephson junction using optimal coupling

Dionisis Stefanatos, Emmanuel Paspalakis

Published Jul 15, 2020• 16 citations
arXivHTMLPDF

Abstract

In this paper we use time-dependent Josephson coupling to enhance unconventional photon blockade in a system of two coupled nonlinear bosonic modes which are initially loaded with weakly populated coherent states, so the evolution is restricted to the manifold of up to two field quanta. Using numerical optimal control, we find the optimal coupling which minimizes the two-photon occupation of one mode, which is actually transferred to the other, while maintaining a nonzero one-photon occupation in the same mode. Moreover, we choose for the continuous coupling to vanish after the transfer between the modes such that they are decoupled and one of them is left only with some one-photon population which can be observed upon its decay. We numerically find lower values of the second-order correlation function obtained at earlier times than with constant coupling, with larger one-photon populations and for longer time windows, corresponding thus to higher emission efficiency and easier detection. The presented methodology is not restricted to the system under study, but it can also be transferred to other related frameworks, to find the optimal driving fields which can improve the single-photon emission statistics from these systems.

DOI
10.1103/physreva.102.013716

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In this paper we use time-dependent Josephson coupling to enhance unconventional photon blockade in a system of two coupled nonlinear bosonic modes which are initially loaded with weakly populated coherent states, so the evolution is restricted to the manifold of up to two field quanta. Using numerical optimal control, we find the optimal coupling which minimizes the two-photon occupation of one mode, which is actually transferred to the other, while maintaining a nonzero one-photon occupation in the same mode. Moreover, we choose for the continuous coupling to vanish after the transfer between the modes such that they are decoupled and one of them is left only with some one-photon population which can be observed upon its decay. We numerically find lower values of the second-order correlation function obtained at earlier times than with constant coupling, with larger one-photon populations and for longer time windows, corresponding thus to higher emission efficiency and easier detection. The presented methodology is not restricted to the system under study, but it can also be transferred to other related frameworks, to find the optimal driving fields which can improve the single-photon emission statistics from these systems.
In this article we consider a bosonic Josephson junction, a model system composed by two coupled nonlinear quantum oscillators which can be implemented in various physical contexts, initially prepared in a product of weakly populated coherent states. We quantify the maximum achievable entanglement between the modes of the junction and then use shortcuts to adiabaticity , a method developed to speed up adiabatic quantum dynamics, as well as numerical optimization, to find time-dependent controls (the nonlinearity and the coupling of the junction) which bring the system to a maximally entangled state.
Abstract Photon blockade in weakly nonlinear resonators is often limited by a trade-off among antibunching, resonant excitation, and tunability. We consider a driven two-mode bosonic system coupled by photon-pair exchange. The exchange interaction vanishes in the one-photon manifold but couples the target and auxiliary two-photon states. Destructive interference can therefore suppress the leading target two-photon amplitude without detuning the target mode. In the weak-drive limit, we derive the required drive-amplitude ratio and relative phase, together with the leading correction due to an auxiliary-mode Kerr shift. Steady-state master-equation calculations confirm the analytical condition and quantify the effects of finite drive, loss asymmetry, pair mismatch, residual nonlinearities, single-photon hopping, dephasing, phase fluctuations, and thermal occupation. Under the stated matched linewidth, coherent-drive, and nonlinear-resource convention, the resonant pair-exchange scheme yields a target single-photon population approximately 9.5 times that of an optimized canonical Kerr-UPB benchmark at g a ( 2 ) ( 0 ) ⩽ 10 − 2 . A normalized post-fabrication recovery test further shows that external-drive recalibration restores the interference minimum across the sampled uncertainty window. These results support photon-pair exchange as a controllable route to continuous-wave resonant antibunched emission.
The photon blockade is a key quantum-nonlinear effect in which the admission of a second photon to a resonator is inhibited, enabling on-demand single-photon emission. Its practical use is limited by the weak intrinsic nonlinearity of most optical platforms. We address this limitation in a coupled-cavity architecture by engineering two-photon dissipation as a control resource rather than a detrimental loss. Within a quantum-master-equation framework, we model single-photon loss, engineered two-photon decay, and pure dephasing, and analyze their joint impact on the steady-state statistics of the driven cavities. We track the zero-delay correlation, photon populations, and detuning/drive dependences under distinct driving schemes (both cavities driven vs. single-cavity drive with. The results show that adding two-photon dissipation (i) suppresses multiphoton occupation and strengthens antibunching, (ii) broadens the operating window in detuning and drive amplitude, and (iii) improves robustness against moderate dephasing and device imperfections. A mechanism analysis attributes these gains to interference between coherent second-order processes and dissipative selection that stabilizes the odd-photon manifold. The study yields design guidelines for realizing stable, cavity-based single-photon sources using dissipation engineering.
We have observed the unconventional photon blockade effect for microwave photons using two coupled superconducting resonators. As opposed to the conventional blockade, only weakly nonlinear resonators are required. The blockade is revealed through measurements of the second order correlation function g^{(2)}(t) of the microwave field inside one of the two resonators. The lowest measured value of g^{(2)}(0) is 0.4 for a resonator population of approximately 10^{-2} photons. The time evolution of g^{(2)}(t) exhibits an oscillatory behavior, which is characteristic of the unconventional photon blockade.
The photon blockade phenomenon, a promising tool for realizing efficient single-photon sources, is the central focus of our work. We study this phenomenon within the context of the multimode extension of the Jaynes-Cummings model, incorporating two-photon dissipation and external coherent driving. Operating in the weak-driving regime, we confine our analysis to the two-excitation sector of the Hilbert space, initially exploring the single-mode case and then focusing on the corresponding multimode problem. Our study calculates the second-order correlation function (both numerically and analytically) for zero- and nonzero time delays in single- and multimode cases, to pinpoint and validate the conditions that lead to conventional and unconventional photon blockade. Our zero delay findings reveal that photon antibunching is comparable in both cases; however, the multimode case offers a greater degree of control and applicability. Furthermore, for non-zero delay operation, we find that when one of the multiple modes is set at the optimal conventional photon blockade conditions, the behavior of the curve mimics the single-mode problem with an overall slower rate of reaching the g(2)(τ)=1g^{(2)}(τ)=1g(2)(τ)=1 value. These results highlight the practical implications of our findings for building useful single-photon sources.