[Paper Review] Quantum gate for Q switching in monolithic photonic bandgap cavities containing two-level atoms

Andrew D. Greentree, J. Salzman+2 more|arXiv (Cornell University)|Nov 11, 2005

Photonic and Optical Devices4 citations

TL;DR

This paper proposes a solid-state quantum gate for Q-switching in monolithic photonic bandgap cavities using tunable two-level atoms, where a control atom in a gate cavity modulates photon transfer to a waveguide via resonant coupling. The scheme enables on-demand, transform-limited single-photon emission with high fidelity by adiabatically tuning the atomic transition to trigger photon ejection, achieving a residual population of 10⁻⁴ and a switching time of ~1 ns.

ABSTRACT

Photonic bandgap cavities are prime solid-state systems to investigate light-matter interactions in the strong coupling regime. However, as the cavity is defined by the geometry of the periodic dielectric pattern, cavity control in a monolithic structure can be problematic. Thus, either the state coherence is limited by the read-out channel, or in a high Q cavity, it is nearly decoupled from the external world, making measurement of the state extremely challenging. We present here a method for ameliorating these difficulties by using a coupled cavity arrangement, where one cavity acts as a switch for the other cavity, tuned by control of the atomic transition.

Motivation & Objective

• To address the challenge of controlling high-Q photonic bandgap cavities in monolithic solid-state systems, where strong coupling limits external access and measurement.
• To develop a scalable, all-solid-state solution for on-demand single-photon generation suitable for quantum information devices.
• To enable Q-switching in monolithic PBG cavities without mechanical or thermal actuation, using only atomic frequency tuning via external fields.
• To demonstrate a practical, experimentally feasible architecture using nitrogen-vacancy centers in diamond-based photonic crystals.

Proposed method

• A coupled cavity system is used, with one cavity as the storage cavity and a second as a tunable gate cavity, both containing a single two-level atom.
• Photon hopping between the cavities is mediated by evanescent coupling, with the gate cavity coupled to a waveguide for outcoupling.
• The atomic transition frequency in the gate cavity is tuned via an external Stark shift, enabling dynamic control of the resonance condition.
• Adiabatic tuning of the atomic frequency brings the gate cavity into resonance with the storage cavity, triggering rapid photon transfer to the waveguide.
• The system is modeled using a Hamiltonian with Rabi coupling terms and decay rates, with dynamics solved under the rotating wave approximation.
• The scheme relies on the good cavity limit, where photon loss is dominated by hopping to the waveguide, not intrinsic cavity decay.

Experimental results

Research questions

• RQ1 Can a monolithic photonic bandgap cavity be effectively Q-switched using only post-fabrication control of atomic transition frequencies?
• RQ2 How can high-fidelity, on-demand single-photon emission be achieved in a solid-state cavity-QED system without mechanical or thermal actuators?
• RQ3 What are the required coupling and decay parameters to achieve efficient, adiabatic photon transfer with minimal residual population?
• RQ4 Can the scheme be realized in a practical platform such as diamond with nitrogen-vacancy centers?

Key findings

• The scheme achieves a residual population of 10⁻⁴ in the storage cavity when not switched, ensuring minimal leakage during the hold phase.
• Photon ejection occurs in approximately 1 ns, corresponding to a switching time of 1/𝐽 ≈ 10⁻⁹ s, with a total switching duration of 2×10⁴π/Ω.
• With Ω = 10¹⁰ Hz, the required detuning δ ≤ 10¹² Hz ensures κcq/δ ≤ 10⁻², satisfying the adiabaticity condition.
• The storage cavity Q is ~10⁵ and the gate cavity Q is ~10⁴, achievable in diamond-based photonic crystals with current fabrication capabilities.
• The system remains robust under realistic parameters, with proof-of-principle operation possible at lower Q values by relaxing adiabaticity and increasing detuning.
• The proposed architecture is experimentally feasible using nitrogen-vacancy centers in diamond, where Stark tuning ranges of ~10¹² Hz exceed the required tuning window.