%0 Journal Article %J Phys. Rev. Lett. %D 2019 %T Photon pair condensation by engineered dissipation %A Ze-Pei Cian %A Guanyu Zhu %A Su-Kuan Chu %A Alireza Seif %A Wade DeGottardi %A Liang Jiang %A Mohammad Hafezi %X

Dissipation can usually induce detrimental decoherence in a quantum system. However, engineered dissipation can be used to prepare and stabilize coherent quantum many-body states. Here, we show that by engineering dissipators containing photon pair operators, one can stabilize an exotic dark state, which is a condensate of photon pairs with a phase-nematic order. In this system, the usual superfluid order parameter, i.e. single-photon correlation, is absent, while the photon pair correlation exhibits long-range order. Although the dark state is not unique due to multiple parity sectors, we devise an additional type of dissipators to stabilize the dark state in a particular parity sector via a diffusive annihilation process which obeys Glauber dynamics in an Ising model. Furthermore, we propose an implementation of these photon-pair dissipators in circuit-QED architecture. 

%B Phys. Rev. Lett. %V 123 %8 04/02/2019 %G eng %U https://arxiv.org/abs/1904.00016 %N 063602 %R 10.1103/PhysRevLett.123.063602 %0 Journal Article %J Nat. Commun. %D 2018 %T Thermal management and non-reciprocal control of phonon flow via optomechanics %A Alireza Seif %A Wade DeGottardi %A Keivan Esfarjani %A Mohammad Hafezi %X

Engineering phonon transport in physical systems is a subject of interest in the study of materials and plays a crucial role in controlling energy and heat transfer. Of particular interest are non-reciprocal phononic systems, which in direct analogy to electric diodes, provide a directional flow of energy. Here, we propose an engineered nanostructured material, in which tunable non-reciprocal phonon transport is achieved through optomechanical coupling. Our scheme relies on breaking time-reversal symmetry by a spatially varying laser drive, which manipulates low-energy acoustic phonons. Furthermore, we take advantage of recent developments in the manipulation of high-energy phonons through controlled scattering mechanisms, such as using alloys and introducing disorder. These combined approaches allow us to design an acoustic isolator and a thermal diode. Our proposed device will have potential impact in phonon-based information processing, and heat management in low temperatures. 

%B Nat. Commun. %V 9(1) %8 2018/3/23 %G eng %U https://arxiv.org/abs/1710.08967 %N 1207 %R https://doi.org/10.1038/s41467-018-03624-y