The processor, codenamed “Hilbert” will be based upon ColdQuanta’s cold atom technology. This technology utilizes Cesium atoms arranged in a 2D 11×11 grid that are supercooled to microkelvin temperatures using lasers. The qubits are spaced apart by a distance of 2-3 microns to provide a very dense layout which has the potential for significant scaling in the future.
The qubits are controlled with multiple lasers which are used to cool the atom, place them in the grid locations, provide controls to implement the qubit gates, and measure the results. Pictures of some of the components used in Hilbert are shown below.
The cold atom approach has several potential advantages and ColdQuanta states they think this makes it highly scalable. First, the qubit density on the chip is very high. Not only is the qubit spacing several orders of magnitude denser than superconducting circuits, it is even denser than trapped ion technology because the cold atoms are electrically neutral while trapped ions are charged and must be separated by a distance to reduce unwanted interactions between qubits due to coulomb force. The cold atom technology would be able to pack a million qubits on a chip that is sized at only 4 square millimeters. In addition, because the system uses laser cooling instead of dilution refrigerators, ColdQuanta’s machine will avoid the cost of a dilution refrigerator which can be hundreds of thousands of dollars. ColdQuanta has indicated they will be building a version with over 1000 qubits within the next three years.
The initial Hilbert machine will be installed at ColdQuanta headquarters in Boulder, Colorado and accessible to customers over the cloud. Hilbert can be programmed using IBM’s open source Qiskit software platform with a backend module that can interface it to Hilbert. ColdQuanta is investigating additional options for both cloud access and software platforms. They have also stated they will be selling a second unit to a customer in 2022.
The performance characteristics of Hilbert are still preliminary. But early results show one qubit gate fidelity at 99.1% and two qubit gate fidelity at 95% with very good coherence times and gate delays in the 500 nanosecond range for a two qubit gate. Each qubits will have a connectivity to eight nearby qubits which is better than the superconducting machines, not quite as good as the ion trap machines which have all-to-all connectivity. Besides increasing the number of qubits, ColdQuanta is working to improve these performance metrics with goals of reaching gate fidelities in the 99.9% range and long range connectivities greater than 50.
When ColdQuanta’s Hilbert machine comes online later this year it will represent another modality of quantum technology and it will be interesting to see how it performance versus the other quantum machines available at that time. The cold atom technology does promise several advantages over the other approaches, but as they say, the proof is in the pudding and we shall see if the resulting machine holds up to its promise.
You can read ColdQuanta’s press release with their announcement here. Also, ColdQuanta has provided some excellent material that explains the operation of Hilbert in more detail. You can view a technology deep dive presentation here and a YouTube video with Dr. Mark Saffman, ColdQuanta’s Chief Scientist, that explains the operation of the processor here.
July 7, 2021