Chiral Discrimination on Gate-Based Quantum Computers

TL;DR

The paper addresses the challenge of performing enantioselective chiral discrimination on gate-based quantum computers by translating STIRAP and STAP control into digital quantum gates. It discretizes Gaussian pulses via Trotterization and maps a three-level molecular system onto a two-qubit register, validating the approach with state-vector simulations and IBM hardware, and comparing STIRAP versus STAP performance. A key contribution is demonstrating that STAP, with counterdiabatic pulses, achieves faster, higher-fidelity enantio-discrimination on a real molecule (1,2-propanediol) while maintaining robustness to hardware noise, enabling practical quantum simulations of chiral dynamics. The work provides a scalable framework for simulating and manipulating molecular chirality on near-term quantum devices, with implications for studying larger degenerate systems and reaction pathways.

Abstract

We present a novel approach to chiral discrimination using gate-based quantum processors, addressing a key challenge in adapting conventional control techniques using modern quantum computing. Schemes such as stimulated rapid adiabatic passage (STIRAP) and shortcuts to adiabaticity (STAP) have shown strong potential for enantiomer discrimination; their reliance on analog and continuous-time control makes them incompatible with digital gate-based quantum computing architectures. Here, we adapt these protocols for quantum computers by discretizing their Gaussian-shaped pulses through Trotterization. We simulate the chiral molecule 1,2-propanediol and experimentally validate this gate-based implementation on IBM quantum hardware. Our results demonstrate that this approach is a viable foundation for advancing chiral discrimination protocols, preparing the way for quantum-level manipulation of molecular chirality on accessible quantum architectures.

Figures (14)

• Figure 1: Closed-loop coupling scheme between three discrete energy states for L and R enantiomers. The Rabi frequencies $\Omega_{P}(t)\space$, $\Omega_{S}(t)\space$, and $\Omega_{Q}(t)$ correspond to the $P-$, $S-$, and $Q-$pulses, respectively.
• Figure 2: (a)–(b) Parametrized implementation of the Q--P--S pulse sequence realizing the proposed discrete Trotter evolution. Both panels depict the same logical sequence at different abstraction levels. The protocol begins from the encoded logical state $\ket{00}_L$ (or $\ket{00}_R$), which corresponds to the physical ground state ($J=0$) for both enantiomers (Eq.\ref{['Eq.35']}), and evolves under the time-dependent Hamiltonians $H_Q(t)$, $H_P(t)$, and $H_S(t)$, with each sub-step duration $\delta t$. (a) Conceptual flow diagram showing the logical evolution $\ket{00}_L \!\rightarrow\! \frac{1}{\sqrt{2}}(\ket{00}_L - \ket{10}_L) \!\rightarrow\! \ket{10}_L$ and $\ket{00}_R \!\rightarrow\! \frac{1}{\sqrt{2}}(\ket{00}_R + \ket{10}_R) \!\rightarrow\! a\ket{00}_R+b\ket{11}_R$. The Q-pulse (blue) applies a conditional single-qubit rotation $R_y(\theta = \pm \Omega_Q \delta t)$ corresponding to $U_Q^{(i)} = \prod_{i=1}^{k} e^{-iH_Q(t_i)\delta t}$. The subsequent P-pulse (green) performs entangling operations $R_{XX}(\Omega_P\delta t/2)$ and $R_{YY}(-\Omega_P\delta t/2)$ generated by $U_P^{(i)} = \prod_{i=1}^{m-k} e^{-iH_P(t_i)\delta t}$, followed by the S-pulse (orange) with $R_{XX}(\Omega_S\delta t/2)$ and $R_{YY}(\Omega_S\delta t/2)$ governed by $U_S^{(i)} = \prod_{i=1}^{m-k} e^{-iH_S(t_i)\delta t}$. (b) Gate-level quantum-circuit representation implementing the same parameterized operators using native rotations and measurement qubits. All gates are explicitly parameterized by their instantaneous Rabi frequencies $\Omega_{Q,P,S}(t_i)$ and step time $\delta t$, ensuring full consistency with the discrete Trotterized propagator $U(t)\!\approx\!\prod_i e^{-iH(t_i)\delta t}$.
• Figure 3: Solid lines show the continuous Gaussian envelopes: $\Omega_{Q}(t)$ (blue), $\Omega_{P}(t)$ (orange), and $\Omega_{S}(t)$ (green). In contrast, dashed lines depict their Trotter decompositions into steps of fixed duration $\delta t$, preserving the integrated pulse area.
• Figure 4: Chiral discrimination of L and R enantiomers using the Stimulated Raman Adiabatic Passage (STIRAP) scheme. Exact diagonalization with QuTiP (blue solid), the statevector simulator (red dashed), and quantum processor experiments (yellow solid) are shown. Panels (a) and (b) show benchmarking of the exact diagonalization results with (ibm_kingston and ibm_fez) quantum processors.
• Figure 5: Time evolution of L and R enantiomers under Stimulated Raman Adiabatic Passage (STIRAP ) protocol for $|00\rangle\space\text{(blue)}$, $|11\rangle \text{(red)}$, and $|10\rangle \text{(green)}$ states, obtained from: (i) exact diagonalization using QuTip $(P^{(\text{QuTip})})$, (ii) statevector simulator of the discretized quantum circuit $(P^{(\text{SV})})$, and (iii) benchmarking of the exact diagonalization results with quantum processors $(P^{(\text{QP})})$.