Fault-tolerant quantum computation by anyons

Fault-tolerant quantum computation by anyons

February 1, 2008 | A. Yu. Kitaev
Fault-tolerant quantum computation using anyons is a promising approach for building a quantum computer that is inherently resistant to errors. Anyons are quasiparticles that exist in two-dimensional systems and exhibit exotic statistics, meaning their wavefunction acquires a phase factor when one anyon moves around another. This property allows for fault-tolerant quantum operations, as the physical nature of anyons inherently protects against certain types of errors. A quantum computer based on anyons can perform complex computations, such as factoring large numbers and solving discrete logarithms, which are infeasible for classical computers. However, achieving fault tolerance in quantum systems is challenging due to decoherence and systematic errors in unitary transformations. Kitaev's work shows that fault-tolerant quantum computation is theoretically possible, with subsequent improvements in error correction and threshold values. In the context of anyons, a quantum code called the toric code is used to encode quantum information. This code is based on a lattice on a torus and uses stabilizer operators to protect quantum states. The ground state of the corresponding Hamiltonian is degenerate, and this degeneracy is robust to local perturbations. The degeneracy is related to the topology of the surface on which the lattice is embedded, and the energy gap between the ground state and excited states ensures that errors can be corrected. Anyons can be classified into abelian and non-abelian types. Abelian anyons, such as those in the fractional quantum Hall effect, have phase factors when braided, while non-abelian anyons, which are more complex, can realize universal quantum computation through braiding. The key idea is that the braiding of non-abelian anyons can be used to perform quantum gates, which are essential for quantum computation. The model based on group algebras allows for the construction of non-abelian anyons, which can be used to create a universal quantum computer. These anyons are described by the quantum double of a group, and their braiding and fusion rules are similar to those in gauge field theories. The protected subspace of the code is not accessible by local measurements and is robust to local perturbations, making it an ideal place to store quantum information. The algebraic structure of the model includes local operators and ribbon operators that can create and manipulate anyons. These operators are essential for performing quantum operations and ensuring fault tolerance. The protected space of the code is characterized by irreducible representations of the quantum double, and the braiding of anyons can be used to perform unitary transformations. In summary, fault-tolerant quantum computation using anyons leverages the unique properties of anyons to protect quantum information from errors. The toric code and other models based on anyons provide a framework for encoding and manipulating quantum information in a way that is inherently resistant to errors, making them a promising approach for building fault-tolerant quantum computers.Fault-tolerant quantum computation using anyons is a promising approach for building a quantum computer that is inherently resistant to errors. Anyons are quasiparticles that exist in two-dimensional systems and exhibit exotic statistics, meaning their wavefunction acquires a phase factor when one anyon moves around another. This property allows for fault-tolerant quantum operations, as the physical nature of anyons inherently protects against certain types of errors. A quantum computer based on anyons can perform complex computations, such as factoring large numbers and solving discrete logarithms, which are infeasible for classical computers. However, achieving fault tolerance in quantum systems is challenging due to decoherence and systematic errors in unitary transformations. Kitaev's work shows that fault-tolerant quantum computation is theoretically possible, with subsequent improvements in error correction and threshold values. In the context of anyons, a quantum code called the toric code is used to encode quantum information. This code is based on a lattice on a torus and uses stabilizer operators to protect quantum states. The ground state of the corresponding Hamiltonian is degenerate, and this degeneracy is robust to local perturbations. The degeneracy is related to the topology of the surface on which the lattice is embedded, and the energy gap between the ground state and excited states ensures that errors can be corrected. Anyons can be classified into abelian and non-abelian types. Abelian anyons, such as those in the fractional quantum Hall effect, have phase factors when braided, while non-abelian anyons, which are more complex, can realize universal quantum computation through braiding. The key idea is that the braiding of non-abelian anyons can be used to perform quantum gates, which are essential for quantum computation. The model based on group algebras allows for the construction of non-abelian anyons, which can be used to create a universal quantum computer. These anyons are described by the quantum double of a group, and their braiding and fusion rules are similar to those in gauge field theories. The protected subspace of the code is not accessible by local measurements and is robust to local perturbations, making it an ideal place to store quantum information. The algebraic structure of the model includes local operators and ribbon operators that can create and manipulate anyons. These operators are essential for performing quantum operations and ensuring fault tolerance. The protected space of the code is characterized by irreducible representations of the quantum double, and the braiding of anyons can be used to perform unitary transformations. In summary, fault-tolerant quantum computation using anyons leverages the unique properties of anyons to protect quantum information from errors. The toric code and other models based on anyons provide a framework for encoding and manipulating quantum information in a way that is inherently resistant to errors, making them a promising approach for building fault-tolerant quantum computers.
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