H. Hainzer, D. Kiesenhofer, T. Ollikainen, Matthias Bock, F. Kranzl, Manoj K. Joshi, Goni Yoeli, Rainer Blatt, Tuvia Gefen, C. F. Roos Correlation spectroscopy with multi-qubit-enhanced phase estimation,
arXiv:2203.12656 arXiv:2203.12656 (ID: 720825)
Precision spectroscopy on trapped-ion crystals subject to correlated dephasing can reveal a multitude of information in the absence of any single-particle coherences. We use correlation spectroscopy for measuring ion-ion distances and transition frequency shifts in one- and two-dimensional ion crystals by analyzing multi-particle correlations of up to N=91 qubits, each of which is encoded in a single ion. Additionally we carry out single-shot measurements of the laser-ion detuning and of path-length fluctuations. We show that the information contained in N-particle correlations reduces the measurement uncertainty as compared to the case where only two-particle correlations are analyzed. We derive quantum precision limits for this problem. While for a pair of qubits entanglement can reduce the measurement uncertainty, entanglement-free correlation spectroscopy becomes asymptotically optimal in the limit of N→∞ when the measurement goal is the determination of all phase differences between the qubits.