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Physical Review A

Steady-state entanglement of harmonic oscillators via dissipation in a single superconducting artificial atom

Fei Wang, Wei Nie, Xun‐Li Feng, C. H. Oh

Published Jul 18, 2016• 17 citations
Publisher

Abstract

The correlated emission lasing (CEL) is experimentally demonstrated in harmonic oscillators coupled via a single three-level artificial atom [Phys. Rev. Lett. 115, 223603 (2015)] in which two-mode entanglement only exists in a certain time period when the harmonic oscillators are resonant with the atomic transitions. Here we examine this system and show that it is possible to obtain the steady-state entanglement when the two harmonic oscillators are resonant with Rabi sidebands. Applying dressed atomic states and Bogoliubov-mode transformation, we obtain the analytical results of the variance sum of a pair of Einstein-Podolsky-Rosen (EPR)-like operators. The stable entanglement originates from the dissipation process of the Bogoliubov modes because the atomic system can act as a reservoir in dressed state representation. We also show that the entanglement is robust against the dephasing rates of the superconducing atom, which is expected to have important applications in quantum information processing.

DOI
10.1103/physreva.94.012330

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The correlated emission lasing (CEL) is experimentally demonstrated in harmonic oscillators coupled via a single three-level artificial atom [Phys. Rev. Lett. 115, 223603 (2015)] in which two-mode entanglement only exists in a certain time period when the harmonic oscillators are resonant with the atomic transitions. Here we examine this system and show that it is possible to obtain the steady-state entanglement when the two harmonic oscillators are resonant with Rabi sidebands. Applying dressed atomic states and Bogoliubov-mode transformation, we obtain the analytical results of the variance sum of a pair of Einstein-Podolsky-Rosen (EPR)-like operators. The stable entanglement originates from the dissipation process of the Bogoliubov modes because the atomic system can act as a reservoir in dressed state representation. We also show that the entanglement is robust against the dephasing rates of the superconducing atom, which is expected to have important applications in quantum information processing.
A single superconducting artificial atom can be used for coupling electromagnetic fields up to the single-photon level due to an easily achieved strong coupling regime. Bringing a pair of harmonic oscillators into resonance with the transitions of a three-level atom converts atomic spontaneous processes into correlated emission dynamics. We present the experimental demonstration of two-mode correlated emission lasing in harmonic oscillators coupled via a fully controllable three-level superconducting quantum system (artificial atom). The correlation of emissions with two different colors reveals itself as equally narrowed linewidths and quenching of their mutual phase diffusion. The mutual linewidth is more than 4 orders of magnitude narrower than the Schawlow-Townes limit. The interference between the different color lasing fields demonstrates that the two-mode fields are strongly correlated.
We show that it is possible to obtain higher-order squeezing and entanglement between a pair of harmonic oscillators coupled to a single Δ-type artificial atom, which is realized because of the broken mirror symmetry of the effective potential in the superconducting circuits. Under the three-photon resonance and adiabatic conditions, the system can act as a coherence-controlled atomic reservoir, resulting in the generation of higher-order nonclassicality at steady state. The stable higher-order nonclassical correlations of the two harmonic oscillators in this solid-state device may find potential applications in quantum communications.
Superconducting quantum bits originally developed for quantum computation have properties similar to real atoms. Because they are micro fabricated circuits, their interaction with electromagnetic radiation can be engineered and effects known from quantum optics may be realized. In this work, a unique lasing scheme exploiting only the lowest two levels of a single artificial atom coupled to a high-quality superconducting resonator is experimentally realized. It is based on the dressing of the atom’s states by a strong signal and the associated rescaling of the relaxation. In addition, basic physical processes are discussed by a separate characterization of the artificial atom, the resonator, and their coupling. A quantum theory including dissipative processes is developed from basic superconducting effects and its applicability demonstrated by a perfect agreement with the experimental results. It gives an illustrative insight into the physics of atom-photon interaction.
In this paper, we reexamine the quantum correlations in a four-state single-atom system in the weak coupling regime, aiming at the realization of stable entanglement and one-way steering via dissipation rather than coherent evolution process. Under the near-resonant conditions, we find out that a single atom can act as a reservoir and behave like a two-level system with a single dissipation channel, through which the composite Bogoliubov mode will evolve into a vacuum state, resulting in the appearance of stationary entanglement between two original modes. In addition, the one-way steering is generated when the symmetry is broken by choosing asymmetrical coupling constants. The present scheme may provide convenience for experimental implement and find applications in quantum information processing.
Abstract Hybrid quantum systems that integrate complementary advantages of different physical platforms provide a new pathway toward large-scale, fault-tolerant quantum information processing. In this work, we theoretically investigate a hybrid system consisting of a Rydberg atom, a piezoelectric nanomechanical resonator, and a superconducting qubit, aiming to achieve high-fidelity steady-state entanglement. In this scheme, the nanomechanical resonator acts as a quantum bus, resonantly coupling to the superconducting qubit via the piezoelectric effect and to the Rydberg atom via the electric dipole interaction. Under the strong-coupling condition, we introduce a dressed-state transformation to analyze the eigenenergy structure of the system. By properly controlling the laser driving fields, the otherwise detrimental dissipation processes are turned into a crucial resource for entanglement preparation. Numerical simulations show that under optimal parameters the fidelity of the target state can reach above 98 % , and the scheme exhibits strong robustness against fluctuations in the driving field strengths and against spontaneous emission noise. This study provides a feasible theoretical approach and technical reference for cross-platform quantum interfaces, distributed quantum computing, and dissipation-assisted quantum state engineering.
We analyze quantum correlations in four-wave mixing in three-level $\ensuremath{\Lambda}$ and V atomic systems by using dressed atomic states and squeeze-transformed cavity modes. Two dissipation channels are identified, through which the dressed atoms simultaneously absorb in the excitations from the pair of squeeze-transformed modes. It is in the presence of two channels that the entanglement is greatly enhanced and the best achievable state approaches the original Einstein-Podolsky-Rosen entangled state. This scheme is applicable in the optical regime where atomic spontaneous emission has to be taken into account, unlike the two-step atomic reservoir engineering scheme, which is limited to the microwave regime.