Speaker
Description
Dicke states, permutationally symmetric superpositions of two-level excitations, are pivotal resources in quantum information science and metrology [1, 2]. Their robust multipartite entanglement makes them ideal candidates for surpassing standard quantum limits in sensing and computation. However, generating arbitrary symmetric states in ion traps, Dicke states being a subset, remains challenging due to the need for precise control in large-scale systems.
We propose experimentally implementing a variational quantum circuit protocol, as described in [3], to prepare Dicke states. The protocol consists of initializing a coherent spin state, then interleaving global one-axis twisting (OAT) gates with global Pauli rotations, optimized variationally to minimize infidelity. Numerical simulations indicate that this method can produce Dicke states, such as $\left| J, M \right\rangle = \left| N/2, 0 \right\rangle$, with infidelities below $10^{-3}$ for a qubit number $N =300$ [3].
In our lab, a 2D crystal of hundreds of trapped Beryllium ions, in a highly optically addressable Penning trap, is a particularly well-suited platform for this protocol. Squeezing is achieved through spin-dependent optical dipole forces (ODF) coupling the ion $2s^2S_{1/2}$ electronic levels (the qubits) to the center-of-mass mode of the crystal (i.e., motional degrees of freedom), generating an effective Ising-type spin-spin interaction that yields entanglement, as demonstrated in large ion ensembles [4, 5]. On the other hand, arbitrary global Pauli rotations are implemented by high-fidelity microwave pulses.
This work provides a path for experimental realization of symmetric states and enables exploration of quantum simulation of Dicke state dynamics in ion trap-based quantum simulators, opening the possibility for simulating systems known for displaying distinctive collective physical phenomena [3].
[1] Marconi et al., arXiv:2506.10185 (2025).
[2] Kitagawa, M. and Ueda, M., Phys. Rev. A 47, 5138 (1993).
[3] Bond et al., arXiv:2312.05060 (2025).
[4] Bohnet et al., Science 352, 1297 (2016).
[5] Pham et al., arXiv:2401.17742 (2024).
