Quantum Computing Industry Nears Level 2 Resilience: Logical Qubits Key to Progress.

Hear from Krysta Svore, Principal Research Manager of Microsoft Quantum, on how creating resilient logical qubits is crucial in developing quantum computers and the quantum computing industry. Currently, according to Krysta Svore, the industry is approaching Level 2.

The quantum computing industry is working towards achieving scaled quantum computing through three levels: Foundational, Resilient, and Scale. Currently, all technologies are at Level 1. The next step, Level 2, involves demonstrating resilient quantum computation on a logical qubit, which requires showing that quantum error correction aids quantum computation. This consists of the interaction between logical qubits and the entanglement they generate. The industry aims to demonstrate two logical qubits performing an error-corrected computation that outperforms the same computation on physical qubits. This would be the first demonstration of resilient quantum computation in the field’s history.

Understanding the Progression of Quantum Computing

Quantum computing is a rapidly evolving field, with the collective goal of achieving scaled quantum computing. To measure progress and develop a robust strategy, the industry has identified three implementation levels: Level 1 Foundational, Level 2 Resilient, and Level 3 Scale. Currently, all quantum computing technologies are at Level 1. The next step towards practical quantum advantage and Level 3 Scale is to demonstrate resilient quantum computation on a logical qubit.

Resilience in this context refers to the ability to show that quantum error correction aids rather than hinders non-trivial quantum computation. However, the interaction between logical qubits and the entanglement it generates is a crucial element of this non-triviality. Therefore, demonstrating two logical qubits performing an error-corrected computation that outperforms the same computation on physical qubits will mark the first demonstration of a resilient quantum computation in the field’s history.

Before the industry can claim success in reaching Level 2 Resilient Quantum Computing, it’s important to agree on what this entails and the path from there to Level 3 Scale.

Defining a Logical Qubit

The most meaningful definition of a logical qubit depends on what one can do with that qubit. A logical qubit is defined such that it initially allows some non-trivial, encoded computation to be performed on it. A significant challenge in formally defining a logical qubit is accounting for distinct hardware. To address this, a set of criteria has been proposed that marks the entrance into the resilient level of quantum computation.

Graduating to Level 2 resilient quantum computing is achieved when fewer errors are observed on the output of a logical, error-corrected quantum circuit than on the analogous physical circuit without error correction. A resilient level demonstration should also include some uniquely “quantum” feature, such as entanglement. Upon satisfaction of these criteria, the term “logical qubit” can then be used to refer to the encoded qubits involved.

The Distinction Between Resilient and Scale Levels

The distinction between the Resilient and Scale levels is worth emphasizing. A proof of principle demonstration of resiliency must be convincing, but it does not require a fully scaled machine. A resilient level demonstration may use certain forms of post-selection, which means the ability to accept only those runs that satisfy specific criteria. However, the chosen post-selection method must not replace error-correction altogether, as error-correction is central to the type of resiliency that Level 2 aims to demonstrate.

Measuring Progress Across Level 2

Once entrance to the Resilient Level is achieved, it’s important to measure continued progress toward Level 3. Progress is proposed to be measured along four axes: universality, scalability, fidelity, and composability. Not every type of quantum computing hardware will achieve Level 3 Scale; the requirements to reach practical quantum advantage at Level 3 include achieving upwards of 1000 logical qubits operating at a mega-rQOPS with logical error rates better than 10-12.

Criteria to Advance from Level 2 to Level 3 Scale

The exit of the resilient level of logical computation will be marked by large-depth, high fidelity computations involving upwards of hundreds of logical qubits. For example, a logical, fault-tolerant computation on ~100 logical qubits or more with a universal set of composable logical operations with an error rate of ~10-8 or better will be necessary. At Level 3, performance of a quantum supercomputer can then be measured by reliable quantum operations per second (rQOPS). A quantum supercomputer will be achieved once the machine is able to demonstrate 1000 logical qubits operating at a mega-rQOPS with a logical error rate of 10-12 or better.

The quantum computing industry is on the brink of reaching the next implementation level, Level 2, which puts the industry on the path to ultimately achieving practical quantum advantage. As a community, there is an opportunity to help measure progress across Level 2, and to introduce benchmarks for the industry.

Quick Summary

The quantum computing industry is working towards achieving practical quantum advantage, which requires graduating through three levels: Foundational, Resilient, and Scale. The next significant step is demonstrating resilient quantum computation on a logical qubit, which involves showing that quantum error correction aids rather than hinders computation, and this has not yet been achieved.

• The quantum computing industry is working towards achieving scaled quantum computing, which involves three implementation levels: Level 1 Foundational, Level 2 Resilient, and Level 3 Scale. Currently, all quantum computing technologies are at Level 1.
• The next step towards practical quantum advantage is to demonstrate resilient quantum computation on a logical qubit. This involves showing that quantum error correction aids rather than hinders non-trivial quantum computation.
• The industry needs to agree on what reaching Level 2 Resilient Quantum Computing entails and the path to Level 3 Scale. This involves defining a logical qubit and setting criteria for entering Level 2.
• A logical qubit is defined as one that allows some non-trivial, encoded computation to be performed on it. The criteria for entering Level 2 include observing fewer errors on the output of a logical, error-corrected quantum circuit than on the analogous physical circuit without error correction, and demonstrating entanglement between at least two logical qubits.
• Once Level 2 is achieved, progress towards Level 3 needs to be measured. This involves assessing universality, scalability, fidelity, and composability of the quantum computing hardware.
• The exit from Level 2 to Level 3 Scale will be marked by large depth, high fidelity computations involving hundreds of logical qubits. A quantum supercomputer will be achieved once the machine can demonstrate 1000 logical qubits operating at a mega-rQOPS with a logical error rate of 10-12 or better.