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    Critical Thought

    Critical thoughts on quantum technologies

    Exciting Advances in Quantum Teleportation Embrace Measurement-Induced Phase Transitions

    ByThemba Hadebe

    Nov 18, 2023
    Exciting Advances in Quantum Teleportation Embrace Measurement-Induced Phase Transitions

    Researchers from Google Quantum AI and Stanford University have made astonishing progress in the realm of quantum mechanics, uncovering a “measurement-induced phase transition” in a quantum system consisting of up to 70 qubits. This remarkable discovery sheds light on the intricate relationship between measurements, interactions, and entanglement in quantum mechanics. Moreover, the researchers have identified a unique form of quantum teleportation that could revolutionize the field of quantum computing.

    1. What is quantum teleportation?
    Quantum teleportation refers to the transfer of an unknown quantum state from one set of qubits to another.

    2. What is a qubit?
    A qubit is the basic unit of quantum information. It is analogous to a classical bit but can exist in a superposition of states, thanks to the principles of quantum mechanics.

    In the study recently published in Nature, the researchers explored how measurements can fundamentally alter the structure of quantum information in space-time. The nature of measurements has a profound impact on the behavior of a quantum system. It has long been a subject of investigation as scientists aim to comprehend its implications for data distribution and organization within quantum computers.

    Quantum mechanics is renowned for its peculiar phenomena, but the role of measurement in this theory is particularly baffling. Since measurements tend to destroy the “quantumness” of a system, they serve as the mysterious bridge between the quantum and classical worlds.

    When dealing with a complex system of qubits, the impact of measurements can lead to drastically different outcomes. It can even give rise to entirely new phases of quantum information. This occurs when interactions and measurements clash. In a quantum system, when qubits interact, their information becomes entangled in a nonlocal manner. However, when the system is measured, the entanglement dissipates. This battle between measurement and interactions results in two distinct phases: one dominated by interactions with widespread entanglement, and another dominated by measurements with suppressed entanglement.

    The groundbreaking research conducted by Google Quantum AI and Stanford University examines the crossover between these two phases, referred to as the “measurement-induced phase transition,” using a system of up to 70 qubits. This represents the largest scale at which measurement-induced effects have been investigated. The researchers have also identified a novel form of quantum teleportation that arises as a consequence of these measurements. This breakthrough could pave the way for innovative techniques in quantum computing.

    Visualization of entanglement within a qubit system is a highly challenging task. The entanglement, represented as an intricate web of connections, is invisible, making it difficult to directly observe. Past experiments have relied on statistical correlations between measurement outcomes to infer the presence of the entanglement web. However, such studies have been constrained by the limitations of small system sizes.

    To overcome these challenges, the researchers employed clever experimental strategies. By rearranging the order of operations, all measurements were conducted at the end of the experiment, simplifying the complexity. Additionally, they devised a new method to measure certain aspects of the entanglement web using a single “probe” qubit. This allowed them to extract more information about the web from fewer experimental runs. Surprisingly, the sensitivity of the probe qubit to external noise became advantageous in this context. The noise sensitivity provided insights into the entanglement of the entire system.

    The team made key observations regarding the impact of measurements on entanglement. In the “disentangling phase,” where measurements dominated over interactions, the entanglement strands remained relatively short. The probe qubit only perceived the noise from its nearest neighbors. In contrast, in the “entangling phase,” where measurements were weaker and entanglement was more prevalent, the probe qubit was sensitive to noise throughout the whole system. The transition between these distinct behaviors marks the sought-after measurement-induced phase transition.

    Furthermore, the researchers demonstrated the emergence of a new form of quantum teleportation resulting from the measurements. By measuring all but two distant qubits in a weakly entangled state, they generated stronger entanglement between those remote qubits. This measurement-induced entanglement across long distances facilitates the observed teleportation.

    The stability of entanglement against measurements in the entangling phase has significant implications for quantum computing. It inspires novel schemes that enhance the robustness of quantum calculations in the presence of noise. The role of measurements in driving new phases and physical phenomena also captivates physicists, offering a new playground for many-body physics and non-equilibrium phenomena.

    In conclusion, the remarkable discoveries made by the researchers at Google Quantum AI and Stanford University in the realm of quantum teleportation and measurement-induced phase transitions open up unprecedented possibilities in the field of quantum computing. This research exemplifies the continuous pursuit of understanding the fundamental principles of the quantum world, and it sets the stage for future breakthroughs in harnessing the power of quantum mechanics.

    “Measurement-induced entanglement and teleportation on a noisy quantum processor” by Google Quantum AI and Collaborators, 18 October 2023, Nature.
    DOI: 10.1038/s41586-023-06505-7