Quantum computing has been hailed as the next breakthrough in computing. Quantum computers are much faster than traditional binary-based computing systems, being able to exploit quantum behaviors to perform complex calculations in a fraction of the time conventional computers and supercomputers can. However, the current generation of quantum computers are prone to errors, in particular leakage errors, meaning that achieving reliable quantum computations is highly challenging.
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Quantum Errors and Challenges
Classical computers are rarely affected by errors, with error rates measured in errors per billion or trillion. Quantum computers, however, are more prone to them, which makes error correction essential for quantum computing to be sustainable. The error rate in current quantum computers is between 0.1% to 1%.1
Quantum computations can be affected by several different types of errors. These include decoherence, noise, and quantum gate imperfections.1 On average, one in every hundred to a thousand quantum gate operations will encounter one of these types of error. Errors in quantum systems can manifest as bit flips, phase flips, or a combination of the two. The fragility of quantum states is the main reason for errors.
Leakage errors are particularly challenging to overcome in quantum computers. This occurs when quantum information leaks out of a qubit’s two computational states into another energy state. This leakage of information occurs over time, spreading throughout multi-qubit interactions. The accumulation of these errors at scale makes error suppression and achieving fault-tolerant quantum computation challenging.2
Atom less is also a problem in quantum systems over time. The calculations in these systems is based on “fuzzy” atoms that can exist in multiple states at once. Quantum properties of the atoms make this possible. However, over time, as the atoms interact with their environment, they can lose their fuzziness, leading to them occupying only one quantum state.
Recent Breakthroughs in Leakage Error Correction
A paper published in 2023 in Nature Physics demonstrated a technique that can shorten leakage lifetime and curtail correlated errors, efficiently returning a quantum system to its computational basis.2
The solution that the researchers came up with is based on a surface code and bit-flip code on a processor. All leakage was removed from the qubits in each computational cycle, and a tenfold reduction in steady-state leakage was achieved.
Another solution is to utilize tunable couplers in quantum systems to overcome leakage errors. Strong frequency tunability can eliminate state leakage on couplers employed in large-scale quantum processors, suppressing state-correlated errors.3
Common error correction methods in quantum systems include utilizing Shor code, Steane code, Surface code, and Hastings-Haah code.1 As mentioned above, surface code has been demonstrated to work well in correcting leakage errors. Furthermore, it is important to maintain quantum coherence during error correction.
Atom Loss and Stability Enhancements
Integrating atom loss mitigation strategies with leakage error correction has the potential to produce more fault-tolerant and robust quantum computing systems. Recent research has demonstrated some progress in producing systems that mitigate the loss of atoms over time.
Scientists at the University of New Mexico and Sandia National Laboratories have demonstrated for the first time an atom loss detection technique in neutral atom platforms. Notably, this can be achieved without disturbing the quantum state of an atom in the system. The researchers have stated that the method they have developed has an accuracy of 93.4%. Errors can be efficiently flagged and corrected.4
The system developed by the researchers uses a code that diagnoses entangling interactions between atoms in the quantum system. The breakthrough came about by accident when researchers realized that the code could detect subtle signals that indicated atomic quantum states without observing them directly. In essence, atom loss could be detected using this approach without damaging the information.4
Employing neutral atoms in quantum systems is one approach that can lead to more robust, leakage-error free quantum computers. Using these atoms, which have no net electric charge, produces more controllable, stable, and, importantly, scalable quantum systems.
Solutions such as trapping neutral atoms in focused laser beams can lead to more stable and robust quantum systems as they are less affected by the environment. Thus, more efficient and effective processing of quantum information can be achieved. Arranging these atoms in reconfigurable arrays leads to robust systems with hundreds of error-free qubits.5
Impact on Quantum Computing Reliability
Correcting leakage errors and detecting and mitigating atom loss improves the reliability of quantum computers by preventing the accumulation of errors over time and leading to further correlated errors.
Suppressing these correlated errors is essential if large scale quantum computers are to be fully realized, as the prevalence of faults compared to conventional supercomputers is a major roadblock to the full commercialization of quantum computers. Recent advances in leakage error correction and atom loss detection are helping to scale up quantum systems and achieve practical quantum supremacy.
In Summary
Correcting errors in quantum computations is a crucial component of fault-tolerant and practical quantum systems. Currently, the prevalence of faults and errors in these systems is proving highly challenging to rectify.
Pinning down a timeline for full-scale quantum computing that could benefit industries and fields such as physics, chemistry, biomedicine, and materials science is difficult. However, with current trends and breakthroughs, some experts predict that this could happen by the end of the decade. Some observers have even stated that quantum computers could enter real-world application by this year.6
Whatever the timescale of practical quantum computing actually turns out to be, it is clear that recent innovations in error detection and correction are significantly impacting the development and deployment of robust, stable, and reliable quantum computers. This could lead to a true computing revolution that impacts multiple sectors of society and future scientific discoveries.
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Further Reading and More Information
[1] Microsoft (2024) Quantum Error Correction [online] Microsoft.com. Available at: https://quantum.microsoft.com/en-us/insights/education/concepts/quantum-error-correction (Accessed on 11 January 2025)
[2] Miao, K.C et al. (2023) Overcoming leakage in quantum error correction Nature Physics 19 pp. 1780-86 [online] Nature.com. Available at: https://www.nature.com/articles/s41567-023-02226-w (Accessed on 11 January 2025)
[3] Yang, X et al. (2024) Coupler-Assisted Leakage Reduction for Scalable Quantum Error Correction with Superconducting Qubits Physical Review Letters 133: 170601 [online] APS Physical Review Journals. Available at: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.133.170601 (Accessed on 11 January 2025)
[4] Chow, M.N.H et al. (2024) Circuit-Based Leakage-to-Erasure Conversion in a Neutral-Atom Quantum Processor PRX Quantum 5: 040343 [online] APS Physical Review Journals. Available at: https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuantum.5.040343 (Accessed on 11 January 2025)
[5] Troutman, K (2024) Neutral Atom Innovations by Quantum Systems Accelerator Mark Quantum Computing Milestones [online] Quantum Systems Accelerator. Available at: https://quantumsystemsaccelerator.org/2024/09/05/neutral-atom-innovations/ (Accessed on 11 January 2025)
[6] Swayne, M (2024) 2025 Expert Quantum Predictions – Quantum Computing [online] Quantum Insider. Available at: https://thequantuminsider.com/2024/12/31/2025-expert-quantum-predictions-quantum-computing/ (Accessed on 11 January 2025)
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