By Yuval Boger
Last year, a group of scientists published papers in Nature which deals with the shuttles between qubits, or as they are called in papers “the coherent transport of entangled atomic arrangements”. The work of this Harvard-led group which includes scientists from QuEra Computing, MIT, and the University of Innsbruck, could prove critical for the development of large-scale quantum computing using neutral atomic arrangements.
The video below shows this back and forth. This is a real video (with the addition of a red ellipse for emphasis), not an animation.
This shows groups of physical qubits that were displaced at the same time. The red circle shows potential entanglement with the nearest qubit at each step.
Coherent shuttle of qubits – the ability to move qubits while maintaining their quantum states – could greatly influence how the next generation of quantum computers can be built. That potential impact can be appreciated in three areas: error correction, multi-zone architecture, and enhancements.
The main challenge in building large-scale quantum computers lies in error management. Unlike classical computing, where information from a single binary digit can be multiplied for error correction, quantum mechanics does not allow such copying (the no-cloning theorem). Therefore, quantum error correction involves spreading information across multiple qubits via entanglement to create redundancy.
The ability to move a qubit while maintaining its state allows qubits that are entangled nearby but then scatter these entangled qubits over a wider area. One error-correction code that involves spreading qubits over an area is the toric code, in which logical qubits are encoded in such a way that they span a two-dimensional lattice. Because the logical qubits are spread over a large area, localized errors affect only a small subset of logical qubits, which makes it possible to correct errors without destroying the entire quantum information. See this article in Nature from Harvard, University of Innsbruck, MIT and AWS, for illustrations of this toric code.
Once qubits can be moved while retaining their state, one can envision the development of a quantum computing architecture that spans multiple zones. For example, you can imagine an architecture with three zones:
- The processing zone where quantum operations are performed on logical qubits.
- The memory zone where the qubits are placed is in a more stable state with a longer coherence time.
- Measurement zones where certain qubits can be measured in the center of a circuit for error correction and conditional execution purposes.
Enabled by alternating qubits, qubits can be moved in and out of this zone as needed.
Beyond the fact that error-corrected qubits allow execution of longer circuits, there are questions about control signals. Control signals are needed to change the state of each qubit as well as to perform multi-qubit operations. However, as one thinks of millions of qubit machines, do we expect to have millions of control signals? Imagine opening up your 4K television and finding that every pixel has a cable. That would be ridiculous. Likewise, alternating qubits allows for an increase in the number of qubits without a matching increase in control signals
Additionally, the qubit shuttle essentially enables any-to-any qubit connectivity. This is in contrast to a fixed layout configuration in which qubits are only connected to their nearest neighbours. Any-to-any connectivity enables circuit compression because information can propagate with less information.
In conclusion, the ability to shuttle between qubits while preserving its quantum state could have far-reaching implications for the future of quantum computing and bring us one step closer to realizing its full potential. These advances open up innovative approaches to error correction, multi-zone architectures, and scaling. This enables a much more flexible, powerful, and efficient quantum computing architecture that can handle complex computations and larger circuits while managing errors more effectively.
Yuval Boger is Chief Marketing Officer for want to, the leader in quantum computers based on neutral atoms. QuEra 256-qubit computers are available for public access on Amazon Braket.
May 17, 2023