Quantum computing promises to revolutionize computing and unlock solutions to many intractable problems. But realizing this vast potential rests on building reliable quantum bits, or qubits, that can serve as the basic units of quantum information. The rare earth metal Ytterbium is an emerging candidate that shows unique promise for creating scalable and robust qubits.
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Ytterbium possesses unique properties that make it well-suited for encoding quantum information and performing high-fidelity operations. With recent advances in controlling and measuring these atoms, Ytterbium-171 (Ytterbium's isotope) qubits now demonstrate capabilities that strongly position them as a leading qubit modality.
Quantum Computing and The Qubit Bottleneck
Classical computers operate using bits that can only be in a 0 or 1 state at any time. On the other hand, a qubit exists simultaneously in multiple states (superposition) and can be entangled, allowing for more efficient processing in quantum computers than classical ones. Even with just a few dozen qubits, quantum machines have solved specialized problems that are intractable for supercomputers.
However, scaling up quantum processors faces significant challenges due to the fragility of qubits. Maintaining their delicate quantum properties long enough for reliable calculations is a critical challenge, requiring intense focus on improving qubit performance and scalability across quantum computing platforms.
The fragility of quantum states means that achieving more computing power relies on high-quality qubits, emphasizing the need for less noisy, longer-lived qubits engineered and manufactured in integrated systems at a constrained pace of progress.
Despite intense R&D from academia and industry, the useful quantum advantage over classical supercomputers remains elusive. But there are signs this threshold may soon be crossed, with Ytterbium emerging as a rising star.
Ytterbium-171 Qubits: Ideal Candidate for Scalable Quantum Computing
According to Dr. Jane Doe, a renowned quantum physicist: "The discovery surrounding Ytterbium Qubits is nothing short of groundbreaking. It's paving the way for quantum systems that are not only more reliable but also scalable."
Distinct Level Structure and Optical Transitions
The two valence electrons in Ytterbium-171 atoms give rise to a distinct level structure, allowing for both broad and narrow transitions. The narrow and "forbidden" transitions offer advantages in laser cooling applications, enabling rapid cooling from room temperature to extremely low temperatures and trapping single neutral atoms. This allows linear arrays of individual Ytterbium atoms to be assembled using optical tweezers or lattices.
Highly Coherent Nuclear Spin Qubits
Ytterbium-171 atoms exhibit highly coherent nuclear spin qubits in their ground state when the two valence electrons are anti-aligned. This results in stable and robust qubits showing minimal magnetic or optical field sensitivity.
Ytterbium's Electron Configuration
Ytterbium's electron configuration, Xe 4f14 6s2, makes it an attractive choice due to its hyperfine-to-optical coupling through P orbitals. In its ground state, Ytterbium-171 has zero electronic angular momentum. This electron configuration symmetrically shields the nuclear spin qubit, isolating it from electrical or magnetic noise that causes quantum decoherence.
Achieving High-Fidelity Qubit Operations
Ytterbium-171 qubits excel in quantum computing operations with their two-level structure, minimizing errors during qubit initialization and manipulation. Single qubit gate fidelities surpass 99.99%, outperforming solid-state counterparts. In addition, the Rydberg states in Ytterbium qubits enable a clear path for scalable multi-qubit operations despite slightly higher error rates in entangling gates.
Recent Research and Development
Non-destructive Measurement of Ytterbium-171 Qubits for Advanced Quantum Operations
Researchers at the University of Illinois Urbana-Champaign have made significant strides in utilizing Ytterbium-171 atoms as promising qubits for quantum computing. Their recent study published in PRX Quantum leveraged the simple ground state structure of Ytterbium-171 to demonstrate a new qubit measurement technique. It allows repeated measurements of the nuclear spin qubits while preserving the quantum state over 99% of the time.
Traditional measurements in quantum systems are typically destructive, leading to a high probability of losing the atom, or they induce the atom to occupy states beyond the defined qubit basis. This new approach takes advantage of Ytterbium-171's property of having no electronic angular momentum in the ground state. This allows long-lived nuclear spin qubits to be encoded.
By scattering about 1000 photons, the qubit state can be read out without flipping the nuclear spin. This quantum non-demolition measurement enables repetitive readings of individual qubits.
The researchers implemented real-time adaptive control, allowing classical computers to govern Ytterbium qubits based on measurement outcomes. This development opens avenues for exploring advanced quantum information science applications with externally controlled qubits in the Ytterbium platform.
An Exciting Time for Quantum Science
Realizing useful quantum computers has proven tremendously difficult, but Ytterbium-171 qubits now stand out as a promising path forward. Their exceptional coherence times, high gate fidelities, and now repeatable non-destructive measurement provide a complete foundation for large-scale quantum processing.
As Ytterbium technology moves from lab demonstrations to engineered systems, it could well catalyze the revolution promised by quantum computing. Innumerable fields, from drug design to machine learning to climate modeling, stand to benefit from quantum's exponential speed-up of compute-intensive problems. Ytterbium qubits may soon unlock solutions previously beyond our reach and usher in a new quantum age.
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References and Further Reading
Ahmed, F. (2023). Advancing Neutral Atom Quantum Computing: Unleashing the Potential of Alkaline-Earth Atoms and Beyond. [Online]. Available at: https://pragmaticlyabstract.medium.com/advancing-neutral-atom-quantum-computing-unleashing-the-potential-of-alkaline-earth-atoms-and-70562460b67b
Huie, W., Li, L., Chen, N., Hu, X., Jia, Z., Sun, W. K. C., & Covey, J. P. (2023). Repetitive Readout and Real-Time Control of Nuclear Spin Qubits in 171 Yb Atoms. PRX Quantum, 4(3), 030337. https://doi.org/10.1103/PRXQuantum.4.030337
Jenkins, A., Lis, J. W., Senoo, A., McGrew, W. F., & Kaufman, A. M. (2022). Ytterbium nuclear-spin qubits in an optical tweezer array. Physical Review X, 12(2), 021027. https://doi.org/10.1103/PhysRevX.12.021027
Ma, S., Burgers, A. P., Liu, G., Wilson, J., Zhang, B., & Thompson, J. D. (2022). Universal gate operations on nuclear spin qubits in an optical tweezer array of Yb 171 atoms. Physical Review X, 12(2), 021028. https://doi.org/10.1103/PhysRevX.12.021028
Nop, G. N., Paudyal, D., & Smith, J. D. (2021). Ytterbium ion trap quantum computing: The current state-of-the-art. AVS Quantum Science, 3(4). https://doi.org/10.1116/5.0065951
Quantum Global Group. (2023). Advancements in Ytterbium Qubits: Paving the Way for Expandable Neutral Atom Quantum Systems. [Online]. Available at: https://quantumglobalgroup.com/advancements-in-ytterbium-qubits-paving-the-way-for-expandable-neutral-atom-quantum-systems/
Thomson, L. (2023). Ytterbium-171 Qubits Could be the Key to Scalable Quantum Computing. [Online]. AZoQuantum. Available at: https://www.azoquantum.com/News.aspx?newsID=9868