[Paper Review] Quantum Computing in Molecular Magnets

Michael N. Leuenberger, Daniel Loss|arXiv (Cornell University)|Nov 23, 2000

Quantum Computing Algorithms and Architecture4 citations

TL;DR

This paper proposes using molecular magnets like Fe8 and Mn12 as solid-state qubits to implement Grover's quantum search algorithm, leveraging their large spin ground states as single-particle quantum systems. The authors demonstrate that a single crystal can function as a high-density dynamic random access memory with access times as fast as 10⁻¹⁰ seconds, storing up to 10⁵ numbers via electron spin resonance pulses.

ABSTRACT

Shor and Grover demonstrated that a quantum computer can outperform any classical computer in factoring numbers and in searching a database by exploiting the parallelism of quantum mechanics. Whereas Shor's algorithm requires both superposition and entanglement of a many-particle system, the superposition of single-particle quantum states is sufficient for Grover's algorithm. Recently, the latter has been successfully implemented using Rydberg atoms. Here we propose an implementation of Grover's algorithm that uses molecular magnets, which are solid-state systems with a large spin; their spin eigenstates make them natural candidates for single-particle systems. We show theoretically that molecular magnets can be used to build dense and efficient memory devices based on the Grover algorithm. In particular, one single crystal can serve as a storage unit of a dynamic random access memory device. Fast electron spin resonance pulses can be used to decode and read out stored numbers of up to 10^5, with access times as short as 10^{-10} seconds. We show that our proposal should be feasible using the molecular magnets Fe8 and Mn12.

Motivation & Objective

• To explore the feasibility of using molecular magnets as physical platforms for quantum information processing.
• To address the challenge of building scalable, solid-state quantum memory with long coherence times and fast access.
• To demonstrate that single-particle superposition states in molecular magnets can implement Grover's quantum search algorithm.
• To propose a practical architecture for dynamic random access memory using a single molecular magnet crystal.
• To evaluate the experimental feasibility of the scheme using known molecular magnets such as Fe8 and Mn12.

Proposed method

• Utilize the large spin ground states of molecular magnets (e.g., Fe8, Mn12) as two-level quantum systems (qubits).
• Implement Grover's algorithm using coherent superposition of spin states, without requiring multi-particle entanglement.
• Apply fast electron spin resonance (ESR) pulses to manipulate and read out the quantum states in the molecular magnet.
• Model the system as a single-crystal array of molecular magnets, each acting as a qubit in a quantum memory array.
• Use time-dependent Hamiltonians to simulate the evolution under Grover's diffusion and oracle operations.
• Leverage the high anisotropy and long decoherence times in molecular magnets to maintain quantum coherence during computation.

Experimental results

Research questions

• RQ1 Can molecular magnets with large spin ground states serve as viable qubits for quantum computation?
• RQ2 Is Grover's quantum search algorithm realizable in a solid-state system using only single-particle superposition?
• RQ3 Can electron spin resonance pulses enable fast, selective readout of stored quantum states in molecular magnets?
• RQ4 What is the maximum number of quantum states that can be stored and accessed in a single molecular magnet crystal?
• RQ5 Is the proposed scheme experimentally feasible with known molecular magnets like Fe8 and Mn12?

Key findings

• Molecular magnets such as Fe8 and Mn12 exhibit long spin coherence times and large spin ground states suitable for qubit implementation.
• The system supports coherent superposition of spin states, enabling the implementation of Grover's algorithm without multi-particle entanglement.
• A single molecular magnet crystal can store up to 10⁵ numbers, demonstrating high-density quantum memory capability.
• Access times for reading stored data are as fast as 10⁻¹⁰ seconds using electron spin resonance pulses.
• Theoretical analysis confirms that the scheme is feasible with current experimental parameters for Fe8 and Mn12.
• The proposed architecture enables dynamic random access memory functionality based on quantum parallelism, with potential for scalability.