Qudit


In quantum computing, a qudit or quantum dit is the generalized unit of quantum information described by a superposition of d states, where the number of states is an integer equal to or greater than two.

Qudit versus qubit

A qudit, characterized by d=2 states is a qubit.
Qudits with d states greater than 2 can provide a larger Hilbert space, providing more ways to store and process quantum information.

Qudit States

  • Qubit – Qudit with d=2 states
  • Qutrit – Qudit with d=3 states
  • Ququart – Qudit with d=4 states

    Error Correction

is the natural process where quantum information is lost due to environmental interaction and quantum error correction is a technique that actively combats decoherence.
In a paper published by Nature on May 14, 2025 researchers at Yale first demonstrate quantum error correction past the break-even point for higher dimensional qudit systems. The team used GKP bosonic codes to encode qutrits and ququarts in superconducting cavities and optimized the protocol using reinforcement learning. These findings are regarded as a significant step in the creation of more efficient quantum computers and opens new paths for hardware-lean quantum architectures, fault tolerant computation, and compact error protected memories.
In a paper published September 2025, researchers demonstrate a new hybrid method that encodes information in both light and matter using a cat state qudit with d>2 which allows for the detection of photon loss through the parity syndrome by entangling a light pulse with ancillary qubits. This method achieves parallel Bell-pair generation by leveraging the multi-level nature of the qudit.
The first open source qudit stabilizer simulator named "Sdim" was announced November 2025 in a pre-print paper on arXiv.

Qudit Logic Gates

A qudit logic gate is a basic quantum circuit that acts on a qudit.
To achieve a universal qudit gate, a set of gates must include a finite set of single qudit gates and at least one two qudit entangling gate that can create entanglement between qudits.

Qudit Control

Qudit control is the precise navigation of a qudit’s quantum state through engineered signals to perform quantum computations.
In a paper published December 16, 2025 a team of researchers achieved a breakthrough in qudit control by engineering five level qudits through individually addressable transitions between Zeeman sublevels, achieved by combining a large linear Zeeman shift with a state-dependent light shift. Simulations predict state-preparation fidelities of F ≃ 0.99 within ∽1 μs, single-qudit gate fidelities of F ≃ 0.99 with π pulse durations of ∽ 2.5 μs, and fast destructive imaging with durations below 10 μs. These results establish a broadly applicable framework for high-fidelity control of Zeeman sublevel-encoded qudits and a promising platform for scalable qudit-based quantum technologies.

Use In Measurement

Quantum information is traditionally used in Ramsey interferometry, a technique used for precise measurement across various areas of science and technology.
Qudits with d>2 have shown to increase precision and resolution of quantum measurements. Qutrits, for example, have shown to achieve a twofold increase in resolution compared to qubits without any reduction in measurement contrast.