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arXiv:2106.11268

Dipole blockade without dipole-dipole interaction

Chengjie Zhu, Wei Li, Yaping Yang, G. S. Agarwal

Published Jun 21, 2021• 1 citation
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Abstract

The dipole blockade phenomenon is a direct consequence of strong dipole-dipole interaction, where only single atom can be excited because the doubly excited state is shifted out of resonance. The corresponding two-body entanglement with non-zero concurrence induced by the dipole blockade effect is an important resource for quantum information processing. Here, we propose a novel physical mechanism for realizing dipole blockade without the dipole-dipole interaction, where two qubits coupled to a cavity, are driven by a coherent field. By suitably chosen placements of the qubits in the cavity and by adjusting the relative decay strengths of the qubits and cavity field, we kill many unwanted excitation pathways. This leads to dipole blockade. In addition, we show that these two qubits are strongly entangled over a broad regime of the system parameters. We show that a strong signature of this dipole blockade is the bunching property of the cavity photons which thus provides a possible measurement of the dipole blockade. We present dynamical features of the dipole blockade without dipole-dipole interaction. The proposal presented in this work can be realized not only in traditional cavity QED, but also in non-cavity topological photonics involving edge modes.

DOI
10.48550/arxiv.2106.11268

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The dipole blockade phenomenon is a direct consequence of strong dipole-dipole interaction, where only single atom can be excited because the doubly excited state is shifted out of resonance. The corresponding two-body entanglement with non-zero concurrence induced by the dipole blockade effect is an important resource for quantum information processing. Here, we propose a novel physical mechanism for realizing dipole blockade without the dipole-dipole interaction, where two qubits coupled to a cavity, are driven by a coherent field. By suitably chosen placements of the qubits in the cavity and by adjusting the relative decay strengths of the qubits and cavity field, we kill many unwanted excitation pathways. This leads to dipole blockade. In addition, we show that these two qubits are strongly entangled over a broad regime of the system parameters. We show that a strong signature of this dipole blockade is the bunching property of the cavity photons which thus provides a possible measurement of the dipole blockade. We present dynamical features of the dipole blockade without dipole-dipole interaction. The proposal presented in this work can be realized not only in traditional cavity QED, but also in non-cavity topological photonics involving edge modes.
We propose a method for realizing the inhibition of simultaneous excitation of two identical qubits in a single-mode cavity QED system, where two qubits are driven by a coherent field and coupled to a cavity with engineered qubit-cavity interactions. By suitably chosen placements of the qubits in the cavity and by adjusting the relative decay strengths of the qubits and cavity field, we close many unwanted excitation pathways. This leads to an inhibition of the doubly excited state. In addition, we show that these two qubits are strongly entangled over a broad regime of the system parameters. We show that a strong signature of nonexcitation of the doubly excited state is the bunching property of the cavity photons, which thus provides a possible measurement of this nonexcitation. We also present dynamical features of the inhibition of simultaneous excitation of two qubits. The proposal presented in this paper can be realized not only in traditional cavity QED, but also in noncavity topological photonics involving edge modes.
We theoretically study the quantum-interference-induced photon blockade and antiblockade phenomenon in an atom-cavity QED system, where the destructive [constructive] interference between two different transition pathways prohibits [enhances] two-photon excitation. To begin with, we study a single-atom--cavity QED system where the atom or cavity is driven by a coherent pump field. We show that the cavity-driven case will lead to the quantum-interference-induced photon blockade under a specific condition, but such an interference-induced photon blockade cannot be realized in the atom-driven case. This is an important consequence of the pathways possible for the two types of drives. Then, we investigate the two-atom case, and find that an additional transition pathway appears in the atom-driven case. We show that this additional transition pathway results in the quantum-interference-induced photon blockade only when the atomic resonant frequency is different from the cavity mode frequency otherwise antiblockade occurs. Moreover, in this case, the condition for realizing the interference-induced photon blockade is independent of the system's intrinsic parameters, which can be used to generate antibunched photons in both weak and strong coupling regimes.
We theoretically investigate the three-photon blockade phenomenon in a two atoms cavity QED system, where two atoms are driven by a coherent field. In the case of in-phase radiations, we show that the three-photon blockade with bunched two photons can be realized in a small regime of the driving field Rabi frequency. However, in the case of out-of-phase radiations, the one-photon excitations are prohibited due to the destructive interference, and three-photon blockade can be realized in a wide regime of driving field Rabi frequency. In addition, the three-photon blockade phenomenon can be significantly improved. The results presented here show that this two-atom scheme is a good candidate to achieve anti-bunched photon pairs.
We describe a mechanism for a controlled generation of a pure Bell state with correlated atoms that involve two or zero excitations. The mechanism inhibits transitions into singly excited collective states of a two-atom system by shifting them from their unperturbed energies. The shift is accomplished by the dipole-dipole interaction between the atoms. The creation of the Bell state is found to be dependent on the relaxation of the atomic excitation. When the relaxation is not present or can be ignored, the state of the system evolves harmonically between a separable to the maximally entangled state. We follow the temporal evolution of the state and find that the concurrence can be different from zero only in the presence of the dipole-dipole interaction. Furthermore, in the limit of a large dipole-dipole interaction, the concurrence reduces to that predicted for an X-state of the system. A general inequality is found which shows that the concurrence of an X-state system is a lower bound for the concurrence of the two-atom system. With the relaxation present, the general state of the system is a mixed state that under a strong dipole-dipole interaction reduces the system to an X-state form. We find that mixed states admit of lower level of entanglement, and the entanglement may occur over a finite range of time. A simple analytical expression is obtained for the steady-state concurrence which shows that there is a threshold value for the dipole-dipole interaction relative to the Rabi frequency of the driving field above which the atoms can be entangled over the entire time of the evolution.
We theoretically study a quantum destructive interference (QDI)-induced photon blockade in a two-qubit driven cavity quantum electrodynamics system with dipole–dipole interaction (DDI). In the absence of dipole–dipole interaction, we show that a QDI-induced photon blockade can be achieved only when the qubit resonance frequency is different from the cavity mode frequency. When DDI is introduced the condition for this photon blockade is strongly dependent upon the pump field frequency, and yet is insensitive to the qubit–cavity coupling strength. Using this tunability feature we show that the conventional energy-level-anharmonicity-induced photon blockade and this DDI-based QDI-induced photon blockade can be combined together, resulting in a hybrid system with substantially improved mean photon number and second-order correlation function. Our proposal provides a nonconventional and experimentally feasible platform for generating single photons.