Voltage controlled quantum logic with trapped ions
Abstract
In my judgement the proposed research project will significantly accelerate the development of a viable fully scalable quantum computer architecture based on trapped ions. An important difference between the traditional approach to trapped ion quantum computers (as exemplified by the work of Dr. Chris Monroe of Univ. of Maryland and IonQ) and the approach being developed by the University of Sussex team is that the quantum logic gates will be applied to the ions using a combination of local voltage controlled magnetic field gradients and a global microwave field instead of using lasers focused on each ion to drive the logic operations. This new approach allows much better scaling of the numbers of qubits since there is no need for multiple very high quality lasers focused with micron scale accuracy per qubit. Additionally, the global microwave tones needed can be generated using widely available RF technology borrowed from cell phone technology. A second very important advantage of the Sussex approach to scaling up the number of qubits (ions) that the system can utilize is the modularity of the ion traps themselves. Each module is being designed to fit together with like modules in a tiled grid pattern. One of the biggest bottlenecks to scaling up the size of quantum computers in all approaches is the need to transfer quantum information across compute modules. Quantum (not classical) information transfer is necessary in order to allow for the desired exponential scaling (in the number of qubits) of the potential computational power of the full system. In the case of superconducting circuit based systems this will require a fully quantum network connecting the mK-class cryostats that required for each module ~ limiting current technology to the roughly 100-200 qubits that can fit into a single cryostat. Optical quantum networks are being pursued as a method to link multiple trapped ion modules by IonQ and the Lucas group at the University of Oxford. This involves using optical links between the ions on different modules and then using the photons to teleport quantum information between them. The issue with this elegant approach is that the maximum rate such a quantum network link has been demonstrated is currently on the order of 10 Hz. This is due to the lack of efficient and reliable quantum memories that have good optical interfaces that can be used implement the quantum network. Prof. Hensinger~s approach is to design the ion trap modules so that the individual ions can be rapidly shuttled (physically moved) from one module to another with very little added noise. This should allow for straightforward scaling to systems with 1-100 thousand ions and possibly more, see Science Advances 3, e1601540 (2017) for details. Prof. Hensinger and his team have already demonstrated magnetic field gradient/microwave driven trapped ion systems with quantum gate fidelities near the fault-tolerance threshold for the surface code. This project will build upon this research and contribute directly to the design of voltage driven quantum logic modules that are predicted to have fidelities above the error correction threshold and are also highly scalable. By the end of the project, I believe that the Sussex team will be in a position to demonstrate a very high performance prototype quantum computer with a significant number of high quality qubits. The reason for this is that the proposed ONRG research is highly complementary with the research that Prof. Hensinger~s team have performed under support from the US Army Research Office over the last 3-4 years, plus additional research supported by other US government agencies. I have contacted Dr. Sara Gamble and Dr. TR Govindan, the Program Officers at the Army Research Office who are directing ARO s investment into the Sussex team s QC research. We will carefully coordinate our plans over the course of this project in order to maximize the impact of the ONRG/ARO joint investment.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 20, 2019
- Source ID
- N629091912116
Entities
People
- Winfried K. Hensinger
Organizations
- Office of Naval Research
- United States Navy
- University of Sussex