Periodic Reporting for period 2 - COHESiV (Coherent Optomechanical and Hyperfine interactions Engineering with Silicon-Vacancy impurities in diamond for quantum networks)
Okres sprawozdawczy: 2022-02-01 do 2023-01-31
Quantum communications and quantum computing hold great promises respectively in terms of provably secure communications and drastic speedup in processing abilities for certain important tasks, thus allowing the computation of problems that are currently intractable even with the most powerful supercomputers. One of the most promising architectures to implement quantum communications and quantum computing is a quantum network, composed of several information processing nodes connected to one another. To process information, each node contains a set of qubits (quantum bits) that are the basic processing units, analogously to computer bits in today's computers. In order to design such nodes, it is necessary to identify a suitable physical system that can act as a qubit. Certain atomic impurities in diamond, called silicon-vacancy centres and consisting of a single silicon atom replacing two neighbouring carbon atoms of the diamond, are promising candidates. They can process information using their spin, which can be thought of as a small magnet tied to the atomic defect and that obeys the laws of quantum mechanics. Information can be encoded in the spin using photons, single light particles. Once encoded in the spin, the information needs to be processed and shared with other spins. The goal of this project is to leverage the properties of these impurities in order to progress towards the realization of a quantum network node. In particular, silicon-vacancy centres have the particularity of being particularly sensitive to vibrations in the diamond, so we aim to generate such vibrations controllably and use them to control the spin and interact with other spins to transfer information among them on a single chip. This is of particular interest because mechanical vibrations can interact with a wide variety of physical systems that could all play a role in a quantum network node, they would thus act as a mediator between vastly different quantum systems that would otherwise not be able to interact. Another important aspect of quantum information is that it can be very fragile and spins can only retain it reliably for a limited amount of time. Another goal is thus to manage to extend that storage time as much as possible. To do so, we take advantage of the presence of other spins in the diamond that belong to the nuclei of certain carbon atoms. These nuclear spins interact very little with their environment and are thus excellent memories into which information can be stored. We thus aim to study how to transfer information between the silicon-vacancy spin that processes information and nuclear spins that store it, and how information can be stored in multiple nuclear spins as long as possible.
During this project, we have successfully interfaced the spin of a single silicon-vacancy centre with mechanical vibrations, namely surface acoustic waves. Surface acoustic waves are vibrations that only propagate at the surface of a material, like ripples on water. By sending precisely timed bursts of surface acoustic waves to a single silicon-vacancy spin, we could control its quantum state and change it at precise time intervals, as is required for quantum algorithms. Furthermore, we managed to take advantage of the coupling of the silicon-vacancy spin to a nearby nuclear spin to demonstrate the mechanical control of this nuclear spin using similar surface acoustic wave bursts. Furthermore, we could show that a nuclear spin controlled mechanically retains excellent capacities to store information on timescales of tens of milliseconds, which is sufficiently long for many quantum algorithms.
In order to increase this storage time, we have investigated nuclear spins that are located closely to one another in the diamond lattice and form pairs. We could show that such nuclear spin pairs can store quantum information for over a minute thanks to a combination of specific characteristics that considerably increase their insensitivity to their environment.
Finally, we have investigated a recently discovered impurity in diamond, namely the tin-vacancy centre. This impurity shares a lot of similarities with the silicon-vacancy centre and also possesses a spin. However, it displays superior optical properties. We have thus incorporated single tin-vacancy centres into photonic crystal cavities, which are nanostructures. We showed that these cavities could enhance considerably the interaction of the tin-vacancy with light. This is particularly important to use light to transfer information efficiently across a quantum network and connect distant spins.
In order to increase this storage time, we have investigated nuclear spins that are located closely to one another in the diamond lattice and form pairs. We could show that such nuclear spin pairs can store quantum information for over a minute thanks to a combination of specific characteristics that considerably increase their insensitivity to their environment.
Finally, we have investigated a recently discovered impurity in diamond, namely the tin-vacancy centre. This impurity shares a lot of similarities with the silicon-vacancy centre and also possesses a spin. However, it displays superior optical properties. We have thus incorporated single tin-vacancy centres into photonic crystal cavities, which are nanostructures. We showed that these cavities could enhance considerably the interaction of the tin-vacancy with light. This is particularly important to use light to transfer information efficiently across a quantum network and connect distant spins.
All these results contribute to the advancement of quantum technologies based on solid-state platforms. This is the first time that a single nuclear spin is controlled via mechanical vibrations, which will allow the use of nuclear spins as quantum memories for quantum states of mechanical systems for fundamental quantum mechanics experiments and allow their interfacing with other quantum systems through mechanical vibrations. Moreover, this approach requires two to three orders of magnitude less power compared to conventional control methods based on radiofrequency or microwave pulses. Combined with the fact that mechanical control limits cross talk between control channels, such a large power reduction is an important consideration for scaling up this system to multiple spins.
We have shown that nuclear spin pairs display one of the longest coherence times among solid-state platforms. Investigating the mechanisms that allow them to store information for such a long time helps understand how to reduce the sensitivity of quantum systems to their environment and thus make them more robust against errors in quantum algorithms.
Finally, searching for more promising quantum systems such as the tin-vacancy centre and enhancing their connectivity by incorporating them in nanostructures contributes to building the most efficient quantum network node for future quantum communications and quantum computing.
These results were published in the following research articles: Physical Review X 12, 011056 (2022), Physical Review X 12, 011048 (2022) and Applied Physics Letters 118 (23) (2021). They were also presented at international conferences and at seminars, including at national laboratories and to industrial actors active in the field to foster the development of quantum technologies.
We have shown that nuclear spin pairs display one of the longest coherence times among solid-state platforms. Investigating the mechanisms that allow them to store information for such a long time helps understand how to reduce the sensitivity of quantum systems to their environment and thus make them more robust against errors in quantum algorithms.
Finally, searching for more promising quantum systems such as the tin-vacancy centre and enhancing their connectivity by incorporating them in nanostructures contributes to building the most efficient quantum network node for future quantum communications and quantum computing.
These results were published in the following research articles: Physical Review X 12, 011056 (2022), Physical Review X 12, 011048 (2022) and Applied Physics Letters 118 (23) (2021). They were also presented at international conferences and at seminars, including at national laboratories and to industrial actors active in the field to foster the development of quantum technologies.