# Memory-built-in quantum cloning in a hybrid solid-state spin register

## TL;DR

This paper demonstrates a method to clone quantum states from an electron spin to a nuclear spin with high fidelity, enabling long-term storage of the cloned states.

## Contribution

The study introduces a hybrid solid-state spin register that enables cloning with built-in quantum memory at room temperature.

## Key findings

- Quantum states were cloned from an electron spin to a nuclear spin with near-optimal fidelity.
- The nuclear spin memory qubit stored the cloned states for a millisecond at room temperature.
- The memory lifetime exceeded that of the original electron spin state by orders of magnitude.

## Abstract

As a way to circumvent the quantum no-cloning theorem, approximate quantum cloning protocols have received wide attention with remarkable applications. Copying of quantum states to memory qubits provides an important strategy for eavesdropping in quantum cryptography. We report an experiment that realizes cloning of quantum states from an electron spin to a nuclear spin in a hybrid solid-state spin register with near-optimal fidelity. The nuclear spin provides an ideal memory qubit at room temperature, which stores the cloned quantum states for a millisecond under ambient conditions, exceeding the lifetime of the original quantum state carried by the electron spin by orders of magnitude. The realization of a cloning machine with built-in quantum memory provides a key step for application of quantum cloning in quantum information science.