Abstract

We construct quantum error-correcting codes that embed a finite-dimensional code space in the infinite-dimensional Hilbert state space of rotational states of a rigid body. These codes, which protect against both drift in the body's orientation and small changes in its angular momentum, may be well suited for robust storage and coherent processing of quantum information using rotational states of a polyatomic molecule. Extensions of such codes to rigid bodies with a symmetry axis are compatible with rotational states of diatomic molecules, as well as nuclear states of molecules and atoms. We also describe codes associated with general nonabelian compact Lie groups and develop orthogonality relations for coset spaces, laying the groundwork for quantum information processing with exotic configuration spaces.

Highlights

  • Quantum systems described by continuous variables arise in many laboratory settings

  • We develop the theory of molecular codes and generalizations thereof. Laboratory realizations of these coding schemes that improve the coherence times of molecular qubits may still be far off, but we propose laying the foundations for molecular quantum error correction as a challenging goal for the physicists and chemists of the noisy intermediate-scale quantum (NISQ) era [36]

  • Though our work is partially motivated by advances in molecular physics, the coding methods we use are best explained in an abstract group-theoretic framework, which we summarize

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Summary

INTRODUCTION

A microwave resonator in a superconducting circuit or the motional degree of freedom of a trapped ion can be viewed as a harmonic oscillator with an infinite-dimensional Hilbert space. Such continuous-variable systems have potential applications to quantum information processing. A GKP code is a quantum error-correcting code designed to protect against noise that slightly shifts the position or momentum of an oscillator. Couplings between a molecule’s internal degrees of freedom can be readily engineered and utilized These features beg the question of whether it is possible to utilize the rich yet spatially compact molecular Hilbert space for quantum error correction; our work shows that such is the case.

SUMMARY OF OUR FRAMEWORK
EXPERIMENTAL REALIZATIONS
Molecular rotors
Rotational states
Microwave dressing
Crystal fields
Nuclear spin coupling
Spin systems
Many small spins
Many medium spins
Two large spins
Planar rotors
Symmetric molecules
Electronic states
Vibrational states
ERROR-CORRECTION BASICS FOR THE PLANAR ROTOR
A protected qubit
Stabilizer formalism
CSS construction
Partial Fourier transform
Symplectic operations
Logical gates
Diagnosis and recovery
Initialization
MOLECULAR CODES
Code words
Position shifts
Momentum kicks
Logical operators
Check operators
Momentum syndromes
Position syndromes
Normalizable code words
Average momentum
Approximate correctability
Dihedral molecular codes
Other non-Abelian molecular codes
LINEAR-ROTOR CODES
Simplest linear-rotor codes
Combined shifts
Gates and check operators
Non-Abelian subgroup codes
Relation to spherical designs
A QUBIT ON A GROUP
Measurements
VIII. CONCLUSION AND FUTURE WORK
Physical noise
Metrology
Nuclear motion
General groups
Leakage error
Momentum-kick distortion
Weyl relation jaHi jlmni
Example
Poisson summation
Abelian subgroup codes
Non-Abelian subgroups
Symmetric harmonics
Notable examples
Symmetry-adapted bases
Coherent states
Findings
Fiber bundles
Full Text
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