Neutral-atom quantum computation using multi-qubit geometric gates via adiabatic passage

TL;DR

The paper addresses the challenge of implementing scalable, high-fidelity multi-qubit gates in neutral-atom quantum processors amid blockade and laser noise. It introduces adiabatic geometric phase gates based on double-STIRAP in a dark-state manifold, enabling two- and multi-qubit controlled-phase gates without requiring extra laser light on the target atom. Through realistic simulations, the authors report fidelities of approximately $98$–$99\%$ for gate times near $0.6$ microseconds, and they systematically analyze robustness to Rabi fluctuations, finite blockade strength, and positional fluctuations. They further benchmark the gates by simulating Grover's search on 2-, 3-, and 4-qubit systems, illustrating the practical utility and scalability of their approach. Overall, the work provides a physically feasible, scalable pathway toward fault-tolerant quantum computation with neutral atoms using geometric-phase-based gates.

Abstract

Adiabatic geometric phase gates offer enhanced robustness against fluctuations compared to con- ventional Rydberg blockade-based phase gates that rely on dynamical phase accumulation. We theoretically demonstrate two- and multi-qubit phase gates in a neutral atom architecture, relying on a double stimulated Raman adiabatic passage (double-STIRAP) pulse sequence that imprints a controllable geometric phase on the qubit systems. The system is designed in such a way that every atom is individually addressable, and moreover, no extra laser is required to be applied on the target atom while scaling up the system from two- to multi-qubit quantum gates. The gate fidelity has been numerically analyzed by changing the gate operation time, and we find that 98% to 99% fidelity can be achieved for gate time $\simeq$ 0.6 $μ$s. We perform a systematic error analysis, which re- veals that our proposed gates can exhibit strong resilience against fluctuations in Rabi frequencies, finite blockade strength, and atomic position variations. These results establish our approach as a physically feasible and scalable pathway toward fault-tolerant quantum computation with neutral atoms. We simulate Grover's search algorithm for two-, three-, and four-qubit systems with high success probability and thereby demonstrate the utility and scalability of our proposed gates for quantum computation.

Figures (8)

• Figure 1: (a) The control and target atoms are arranged in two different optical traps with a fixed distance $l$ between the trap centers. The laser pulse sequence to complete the gate protocol is shown. (b) When the control atom is at $\ket 0$, the $\ket r$ state is not populated. As a result, there is no shift in the state $\ket R$, the dark state condition forbids any population transfer from the state $\ket{A}$. (c) If the control atom is in $\ket 1$, after the first $\pi$-pulse is applied, $\ket r$ gets populated, resulting in a shift $V$ in $\ket R$. This breaks the dark state condition, initiating population transfer from $\ket A$. After the d-STIRAP process is completed, the state gathers a geometric phase $\Gamma$ as described in the main text. Applying the second $\pi$-pulse on the control atom, we complete the gate protocol.
• Figure 2: Schematic of the evolutions of all four initial states.
• Figure 3: (a),(b) Atomic configuration for three- and four-qubit controlled phase gates, respectively.
• Figure 4: Real part of the amplitude of the target atom state $\ket{A}$ on the completion of the d-STIRAP process is plotted for two different initial states of the control atom. (a) When the control atom is at $\ket{0}$, for $\Omega_c/\Omega_0>2$, population transfer is blocked $>99\%$, i.e. real part of the amplitude does not change. (b) When initially control atom is in $\ket{1}$, real part of the amplitude of $\ket{A}$ changes as increasing $V$, while we fix $\Omega_c=3$.
• Figure 5: Gate fidelities for two, three, and four qubit cases are plotted varying the gate time.