Atom Computing
Recently, quantum computers constructed from arrays of ultracold atoms have become a major contender in the race to produce machines powered by qubits that can surpass their classical counterparts in performance. Although the first completely functional quantum processors to be programmed via the cloud have been produced by alternative hardware architectures, further advancements indicate that atom-based platforms may be superior in terms of future scalability.
This scaling benefit results from the atomic qubits being exclusively cooled, trapped, and manipulated via photonic technology. Neutral-atom quantum computers can be primarily constructed using currently available optical components and systems that have already been optimised for accuracy and dependability, eschewing the need for intricate cryogenic systems or chip fabrication processes.
A physicist at Princeton University in the United States named Jeff Thompson and his team have been developing a quantum computer based on arrays of ytterbium atoms. “The traps are optical tweezers, the atoms are controlled with laser beams and the imaging is done with a camera,” Thompson explains. “The engineering that can be done with the optical system is the only thing limiting the scalability of the platform, and a lot of that work has already been done in the industry of optical components and megapixel devices.”
Enormous atomic arrays
Many attractive properties of neutral atoms make them suitable for quantum information encoding. Firstly, they are all the same, meaning that there is no need to tune or calibrate individual qubits because they are all flawless and devoid of any flaws that could be introduced during creation. Important quantum features like superposition and entanglement are preserved over sufficiently long periods to enable computation, and their quantum states and interactions are likewise well understood and characterised.
The pursuit of fault tolerance
This important development made atomic qubits a competitive platform for digital quantum computing, spurring research teams and quantum companies to investigate and improve the efficiency of various atomic systems. Although rubidium remains a popular option, ytterbium is seen by certain groups to provide some important advantages for large-scale quantum computing. Thompson argues that because ytterbium has a nuclear spin of one half, the qubit can be encoded entirely in the nuclear spin.”They found that pure nuclear-spin qubits can maintain coherence times of many seconds without special procedures, even though all atom- or ion-based qubits havegood coherence by default.”
Examining rational qubits
In the meanwhile, Lukin’s Harvard group has perhaps made the closest approach to error-corrected quantum computing to yet, collaborating with a number of academic partners and the Boston-based startup QuEra Computing. Utilising so-called logical qubits, which distribute the quantum information among several physical qubits to reduce error effects, is a critical advancement.
One or two logical qubits have been produced in previous demonstrations using different hardware platforms, but Lukin and colleagues demonstrated by the end of 2023 that they could produce 48 logical qubits from 280 atomic qubits. They were able to move and operate each logical block as a single unit by using optical multiplexing to illuminate every rubidium atom inside a logical qubit with identical light beams. This hardware-efficient control technique stops mistakes in the physical qubits from growing into a logical defect since every atom in the logical block is treated separately.
The researchers additionally partitioned their design into three functional zones to enable more scalable processing of these logical qubits. The first is utilised to ensure that these stable quantum states are separated from processing mistakes in other sections of the hardware by manipulating and storing the logical qubits, coupled with a reservoir of physical qubits that may be called upon. Next, logical qubit pairs can be “shuttled” into the second entangling zone, where two-qubit gate operations are driven with fidelity exceeding 99.5% by a single excitation laser. Each gate operation’s result is measured in the final readout zone, which doesn’t interfere with the ongoing processing duties.
Future scalability
Another noteworthy development is that QuEra has secured a multimillion-dollar contract at the UK’s National Quantum Computing Centre (NQCC) to construct a version of this logical processor. By March 2025, the national lab will have seven prototype quantum computers installed, including platforms that take advantage of superconducting qubits and trapped ions, as well as a neutral-atom system based on cesium from Infleqtion (previously ColdQuanta). The QuEra system will be one of these systems.
Replenishing the supply of atoms
In order to create a path to larger-scale machines, the Atom Computing team has included additional optical technologies into its revised platform. Bloom states, “They could have just bought some really big lasers if They wanted to go from 100 to 1,000 qubits.” “However, they wanted to get the array on a path where they can keep expanding it to hundreds of thousands or even a million atoms without encountering problems with the laser power.”
Combining the atomic control offered by optical tweezers with the trapping capability of optical lattices which are primarily found in the most accurate atomic clocks in the world has been the solution for Atom Computing. By adding an optical buildup cavity to create constructive interference between multiple reflected laserThese optical lattices can improve their performance by creating a subwavelength grid of potential wells via laser beam interference.”With just a moderate amount of laser power, They can create a huge array of deep traps with these in-vacuum optics,” adds.”They could rise higher, but decided to show an arrangement that traps 1,225 ytterbium.”
