A single trapped atom has revealed a fascinating quantum phenomenon that could revolutionize future computing. This groundbreaking study, led by Dr. Oana Băzăvan at the University of Oxford, showcases a unique form of quantum motion, opening up new possibilities for quantum computing. The experiment demonstrates a rare fourth-order quantum squeezing effect, known as quadsqueezing, alongside two simpler versions. This achievement is significant because it showcases a new way to control delicate quantum behavior, which is crucial for the development of more advanced quantum computers.
The key to this discovery lies in the manipulation of a single charged atom, held nearly still by electric fields. By using lasers, the researchers were able to steer the atom's motion and create a quantum state with four linked units of motion, far surpassing the usual two. This quadsqueezing effect emerged 100 times faster than conventional methods, addressing the challenge of fragile quantum motion fading before the state can be fully built. The speed is essential for the practical implementation of quantum computing.
Quantum motion, described as a quantum harmonic oscillator, is a fundamental concept in physics. It involves systems with evenly spaced energy levels, and ordinary squeezing redistributes quantum uncertainty, making one aspect clearer while the other less certain. This technique has been instrumental in improving measurements at the Laser Interferometer Gravitational-Wave Observatory (LIGO). However, the Oxford study goes beyond this two-way tradeoff, exploring higher-order motion that quantum computers may require.
The team's innovative approach involved combining two controlled laser forces acting on the same ion, a concept known as non-commutativity. This means that the order in which the forces are applied can significantly impact the final outcome. By manipulating laser frequencies, they successfully transitioned from ordinary quantum squeezing to more complex three-part and four-part versions of the effect. This progress is crucial as higher-order states offer unique behaviors that standard calculations cannot easily replicate.
The Wigner function, a mathematical representation of position and momentum information, was used to confirm the states. The researchers rebuilt the ion's quantum motion from measurements, revealing distinct patterns for second-, third-, and fourth-order states. These patterns provided more evidence than a single number, as each state exhibited a different measurable shape. Higher-order states are significant because they enable quantum machines to perform operations that ordinary squeezing and basic movement cannot achieve.
Continuous-variable quantum computing relies on these unusual quantum effects to store information in continuously changing values, rather than simple on-off states. Without these tools, certain parts of the machine remain susceptible to classical computer imitation. The Oxford experiment, however, serves as a clean test bed for controlling motion and spin with fine timing, rather than demonstrating a fully functional quantum computer.
The study's flexibility is evident in a 2021 proposal that mapped a route using spin-motion interactions. By adjusting detuning, the team can select the desired interaction, making the method adaptable beyond a single ion. Scaling this approach could involve controlling multiple motional modes, enabling interactions for simulation, sensing, and error-resistant quantum information. Additionally, spin control could facilitate the creation of specially prepared quantum states during calculations, enhancing their efficiency.
Dr. Raghavendra Srinivas, a physicist at Oxford's Department of Physics and study supervisor, expresses excitement about the potential discoveries in uncharted quantum territory. The single ion provided a sharper handle on high-order quantum behavior, allowing physicists to control disagreeing forces and create motion. However, the challenge lies in maintaining the speed advantage while scaling up to more particles, modes, and checks.
This research, published in Nature Physics, marks a significant step forward in quantum computing. It highlights the importance of quantum motion control and opens up new avenues for exploration, with the potential to reshape the future of computing.
