Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2411.07137

Experimental evidence for dipole-phonon quantum logic in a trapped calcium monoxide and calcium ion chain

Lu Qi, Evan C. Reed, Yu, Boyan, Kenneth R. Brown

Published Nov 11, 2024• 0 citations
arXivHTMLPDF

Abstract

Dipole-phonon quantum logic (DPQL) offers novel approaches for state preparation, measurement, and control of quantum information in molecular ion qubits. In this work, we demonstrate an experimental implementation of DPQL with a trapped calcium monoxide and calcium ion chain at room temperature. We present evidence for one DPQL signal in two hours of data collection. The signal rises clearly above the characterized noise level and has a lower bound on the statistical significance of 4.1$σ$. The rate of observation is limited by the low thermal population in the molecular ground rotational state.

DOI
10.48550/arxiv.2411.07137

Related papers

Spectroscopy using dipole-phonon quantum logic

Lu Qi, Evan C. Reed, Duanyang Wang +2 more

Dipole-phonon quantum logic (DPQL) offers novel approaches for state preparation, measurement, and control of quantum information in molecular ion qubits. Here we report the first experimental demonstration of DPQL as a spectroscopic tool using the shared motional mode of a CaO$^+$-Ca$^+$ ion chain to measure the frequency splitting of the ground $Ω$-doublet of CaO$^+$. By comparing the dipole-phonon signal across three trap-frequency ramp ranges, we determine the splitting to be $ω_{mol}=2π\times454\pm1$ kHz and place a lower bound on the effective dipole-phonon coupling. The rate of observation is limited by the low thermal population in the molecular ground rotational state.

quant-pharXiv:2610.07680•Oct 7, 2026•0 citations

Dipole-Phonon Quantum Logic with Trapped Polar Molecular Ions

Wesley C. Campbell, Eric R. Hudson

The interaction between the electric dipole moment of a trapped molecular ion and the phonon modes of the confined Coulomb crystal couples the orientation of the molecule to its motion. We consider the practical feasibility of harnessing this interaction to initialize, process, and read out quantum information encoded in molecular ion qubits without ever optically illuminating the molecules. We present two schemes wherein a molecular ion can be entangled with a cotrapped atomic ion qubit, providing, among other things, a means for molecular state preparation and measurement. We also show that virtual phonon exchange can significantly boost the range of the intermolecular dipole-dipole interaction, allowing strong coupling between widely separated molecular ion qubits.

arXiv:1909.02668•Physical Review Letters•Sep 14, 2020•31 citations

Quantum logic control and spectroscopy of a single molecular ion

Alejandra Collopy, David R. Leibrandt, Dietrich G. Leibfried +1 more

Quantum logic enables state preparation, readout and spectroscopy of otherwise difficult-to-study ions. Using the coupled harmonic motion shared between co-trapped ions, information can be transferred from the "spectroscopy" ion to the easily manipulated "logic" ion. With this technique we perform high-resolution terahertz-scale rotational spectroscopy of a single CaH+ molecular ion in pure states by leveraging a Ca+ ion as our logic ion. Entangled states between a CaH+ and a Ca+ have also been demonstrated, making molecular ions possible components of hybrid systems for quantum information processing. Because all our laser operations on the molecule are driving stimulated Raman transitions with high detuning, the technique promises to be generalizable to a wide variety of molecular ion species. Additionally, we study the systematic effects of the trap RF electric field on molecular levels and use it to obtain a measurement of the dipole moment of the charged molecule.

Optical and Quantum Sensing and Precision Metrology•Mar 4, 2021•0 citations

The role of spectator modes in the quantum-logic spectroscopy of single trapped molecular ions

Mikolaj Roguski, Aleksandr Shlykov, Ziv Meir +1 more

Quantum-logic spectroscopy has become an increasingly important tool for the state detection and readout of trapped atomic and molecular ions which do not possess easily accessible closed-cycling optical transitions. In this approach, the internal state of the target ion is mapped onto a co-trapped auxiliary ion. This mapping is typically mediated by normal modes of motion of the two-ion Coulomb crystal in the trap. The present study investigates the role of spectator modes not directly involved in a measurement protocol relying on a state-dependent optical-dipole force. We identify a Debye-Waller-type effect that modifies the response of the two-ion string to the force. We show that cooling the spectator modes of the string allows for the detection of the rovibrational ground state of an N$_2^+$ molecular ion with a computed statistical fidelity exceeding 99.99%, improving on previous experiments by more than an order of magnitude while also halving the experimental time. This enhanced sensitivity enables the simultaneous identification of multiple rotational states with markedly weaker signals.

arXiv:2504.02642•Apr 3, 2025•0 citations

The role of spectator modes in the quantum-logic spectroscopy of single trapped molecular ions

Mikolaj Roguski, Aleksandr Shlykov, Ziv Meir +1 more

Abstract Quantum-logic spectroscopy has become an increasingly important tool for the state detection and readout of trapped atomic and molecular ions which do not possess easily accessible closed-cycling optical transitions. In this approach, the internal state of the target ion is mapped onto a co-trapped auxiliary ion. This mapping is typically mediated by normal modes of motion of the two-ion Coulomb crystal in the trap. The present study investigates the role of spectator modes not directly involved in a measurement protocol relying on a state-dependent optical-dipole force. We identify a Debye-Waller-type effect that modifies the response of the two-ion string to the force. We show that cooling the spectator modes of the string allows for the detection of the rovibrational ground state of an $${{{{\rm{N}}}}}_{2}^{+}$$ N 2 + molecular ion with a computed statistical fidelity exceeding 99.99%, improving on previous experiments by more than an order of magnitude while also halving the experimental time. This enhanced sensitivity enables the simultaneous identification of multiple rotational states with markedly weaker signals.

Communications Physics•Nov 25, 2025•0 citations

Dipolar quantum logic for freely rotating trapped molecular ions

Eric R. Hudson, Wesley C. Campbell

We consider the practical feasibility of using the direct, electric dipole-dipole interaction between cotrapped molecular ions for robust quantum logic without the need for static polarizing fields. The use of oscillating dipole moments, as opposed to static electric dipoles, dynamically decouples the dipoles from laboratory fields, including the electric fields of the trap itself. Further, this implementation does not require the quantum control of motion, potentially removing a major roadblock to ion trap quantum computing scalability. Since the polarizing field is electromagnetic radiation, even pairs of states with splittings in the THz regime can be fully polarized.

arXiv:1806.09659•Physical Review A•Oct 25, 2018•61 citations
Dipole-phonon quantum logic (DPQL) offers novel approaches for state preparation, measurement, and control of quantum information in molecular ion qubits. In this work, we demonstrate an experimental implementation of DPQL with a trapped calcium monoxide and calcium ion chain at room temperature. We present evidence for one DPQL signal in two hours of data collection. The signal rises clearly above the characterized noise level and has a lower bound on the statistical significance of 4.1σσσ. The rate of observation is limited by the low thermal population in the molecular ground rotational state.
Dipole-phonon quantum logic (DPQL) offers novel approaches for state preparation, measurement, and control of quantum information in molecular ion qubits. Here we report the first experimental demonstration of DPQL as a spectroscopic tool using the shared motional mode of a CaO+^++-Ca+^++ ion chain to measure the frequency splitting of the ground ΩΩΩ-doublet of CaO+^++. By comparing the dipole-phonon signal across three trap-frequency ramp ranges, we determine the splitting to be ωmol=2π×454±1ω_{mol}=2π\times454\pm1ωmol​=2π×454±1 kHz and place a lower bound on the effective dipole-phonon coupling. The rate of observation is limited by the low thermal population in the molecular ground rotational state.
The interaction between the electric dipole moment of a trapped molecular ion and the phonon modes of the confined Coulomb crystal couples the orientation of the molecule to its motion. We consider the practical feasibility of harnessing this interaction to initialize, process, and read out quantum information encoded in molecular ion qubits without ever optically illuminating the molecules. We present two schemes wherein a molecular ion can be entangled with a cotrapped atomic ion qubit, providing, among other things, a means for molecular state preparation and measurement. We also show that virtual phonon exchange can significantly boost the range of the intermolecular dipole-dipole interaction, allowing strong coupling between widely separated molecular ion qubits.
Quantum logic enables state preparation, readout and spectroscopy of otherwise difficult-to-study ions. Using the coupled harmonic motion shared between co-trapped ions, information can be transferred from the "spectroscopy" ion to the easily manipulated "logic" ion. With this technique we perform high-resolution terahertz-scale rotational spectroscopy of a single CaH+ molecular ion in pure states by leveraging a Ca+ ion as our logic ion. Entangled states between a CaH+ and a Ca+ have also been demonstrated, making molecular ions possible components of hybrid systems for quantum information processing. Because all our laser operations on the molecule are driving stimulated Raman transitions with high detuning, the technique promises to be generalizable to a wide variety of molecular ion species. Additionally, we study the systematic effects of the trap RF electric field on molecular levels and use it to obtain a measurement of the dipole moment of the charged molecule.
Quantum-logic spectroscopy has become an increasingly important tool for the state detection and readout of trapped atomic and molecular ions which do not possess easily accessible closed-cycling optical transitions. In this approach, the internal state of the target ion is mapped onto a co-trapped auxiliary ion. This mapping is typically mediated by normal modes of motion of the two-ion Coulomb crystal in the trap. The present study investigates the role of spectator modes not directly involved in a measurement protocol relying on a state-dependent optical-dipole force. We identify a Debye-Waller-type effect that modifies the response of the two-ion string to the force. We show that cooling the spectator modes of the string allows for the detection of the rovibrational ground state of an N2+_2^+2+​ molecular ion with a computed statistical fidelity exceeding 99.99%, improving on previous experiments by more than an order of magnitude while also halving the experimental time. This enhanced sensitivity enables the simultaneous identification of multiple rotational states with markedly weaker signals.
Abstract Quantum-logic spectroscopy has become an increasingly important tool for the state detection and readout of trapped atomic and molecular ions which do not possess easily accessible closed-cycling optical transitions. In this approach, the internal state of the target ion is mapped onto a co-trapped auxiliary ion. This mapping is typically mediated by normal modes of motion of the two-ion Coulomb crystal in the trap. The present study investigates the role of spectator modes not directly involved in a measurement protocol relying on a state-dependent optical-dipole force. We identify a Debye-Waller-type effect that modifies the response of the two-ion string to the force. We show that cooling the spectator modes of the string allows for the detection of the rovibrational ground state of an N2+{{{{\rm{N}}}}}_{2}^{+}N2+​ N 2 + molecular ion with a computed statistical fidelity exceeding 99.99%, improving on previous experiments by more than an order of magnitude while also halving the experimental time. This enhanced sensitivity enables the simultaneous identification of multiple rotational states with markedly weaker signals.
We consider the practical feasibility of using the direct, electric dipole-dipole interaction between cotrapped molecular ions for robust quantum logic without the need for static polarizing fields. The use of oscillating dipole moments, as opposed to static electric dipoles, dynamically decouples the dipoles from laboratory fields, including the electric fields of the trap itself. Further, this implementation does not require the quantum control of motion, potentially removing a major roadblock to ion trap quantum computing scalability. Since the polarizing field is electromagnetic radiation, even pairs of states with splittings in the THz regime can be fully polarized.