Broadband Population Transfer Based on Suture Adiabatic Pulses

High-fidelity coherent population transfer plays a vital role in the realization of quantum memories. However, population transfer with high performance across a broad frequency range is still challenging due to the finite Rabi coupling strength limited by laser powers. Here we propose a novel population-transfer scheme by suturing adiabatic control pulses with each pulse covering certain frequency interval, which are connected in a way that neighboring adiabatic pulses have opposite chirping directions. Taking the widely utilized hyperbolic-square-hyperbolic pulse as an example, we demonstrate that rapid and robust population transfer can be achieved. The transfer bandwidth scales linearly with the number of suture pulses while maintaining high fidelity, even at the suture points where adiabaticity breaks down. Crucially, these pulses can be realized by a single laser by means of temporal multiplexing. For a given bandwidth, this strategy substantially reduces the operational time which is necessary for on demand read-out and suppressing decoherence effects. Our scheme enables a dramatic increase in multimode storage capacity and paves the way for realizing practical quantum networks.

💡 Research Summary

The paper addresses a central bottleneck in quantum‑memory operation: achieving high‑fidelity population transfer across a broad spectral bandwidth when the available Rabi frequency is limited by laser power. Conventional adiabatic control pulses obey the scaling law W ≈ Ω²τ, meaning that for a fixed maximum Rabi amplitude Ω, the bandwidth W can only be increased by lengthening the pulse duration τ. Longer pulses, however, expose the system to decoherence and reduce overall memory efficiency.

To overcome this limitation the authors introduce “Suture Adiabatic Pulses” (SAP). The idea is to split the total spectral range into n sub‑intervals, each addressed by its own adiabatic control pulse. As a concrete example they use the hyperbolic‑square‑hyperbolic (HSH) pulse, which consists of two hyperbolic edges and a central linear segment. The key design rule is that neighboring pulses have opposite chirp directions: if the first pulse’s instantaneous detuning follows Δ₁(t)=+Δ(t)+f/2, the second follows Δ₂(t)=−Δ(t)−f/2, where f is the frequency span of a single component. This opposite‑chirp arrangement creates constructive interference in the “suture” region where the adiabatic condition formally breaks down, allowing atoms that sit near the boundary to undergo a damped‑oscillation transition rather than a complete loss of fidelity.

Mathematically the total Hamiltonian is written as
H(t)=½(ω₁+δ)σ_z+Ω̅(t)∑_{m=1}^{n}cos