Researchers Make Progress in Building a Practical Quantum Computer

​In an unprecedented move, researchers have created a fully-connected 32-qubit trapped-ion quantum computer register to function at cryogenic temperatures. The new system is a crucial step toward building practical quantum computers.

Jun-ki Kim from Duke University will reveal the new hardware design at the inaugural OSA Quantum 2.0 conference, scheduled as an all-virtual event in partnership with OSA Frontiers in Optics and Laser Science APS/DLS (FiO + LS) conference between the 14th and the 17th of September.

Fully-Programmable Ion Trap Quantum Computers​

Rather than using regular computer bits that can only be a zero or a one, quantum computers employ qubits that can be in superposition of computational states. This enables quantum computers​ to solve problems that are too intricate for traditional computers.

Trapped-ion quantum computers​ are some of the most promising types of quantum technology for quantum computing, but it has been rather difficult to build these computers with sufficient qubits so they can be practical.

“In collaboration with the University of Maryland, we have designed and constructed several generations of fully-programmable ion trap quantum computers,” said Kim. “This system is the latest in the effort where many of the challenges leading to long-term reliability is tackled head-on.”

Improving Quantum Computers

Trapped-ion quantum computers cool ions to incredibly low temperatures, which enables them to be suspended in an electromagnetic field in an ultra-high vacuum and then controlled with accurate lasers to form qubits.

Until now, achieving high computational performance in large-scale ion trap systems has been obstructed by the crashes with background molecules perturbing the ion chain, instability of the laser beams leading the logic gates seen by the ion, and electric field noise coming from the trapping electrodes stirring the ion’s motion regularly used to generate entanglement.

In the new research, Kim and fellow researchers fixed these issues by coming with some dramatically new solutions. The ions are trapped in a localized ultra-high vacuum chamber inside a closed-cycle cryostat cooled to 4K temperatures, with slight vibrations.

This system removes the disturbance of the qubit chain emerging from collisions with residual molecules from the environment, and firmly suppresses the irregular heating from the trap surface.

Solid Progress

To have clean laser beam profiles and reduce errors, the scientists used a photonic crystal fiber to link different parts of the Raman optical system that leads qubit gates, which are the building blocks of quantum circuits.

Moreover, the sensitive laser systems needed to manage the quantum computers​ are created to be taken off the optical table and installed in instrumental racks; the laser beams are then sent to the system in single-mode optical fibers.

The team has found and applied new ways of designing and using optical systems that basically remove mechanical and thermal volatility to create a turn-key laser condition for trapped ion quantum computers​.

Overall, the researchers have proved that the system is able to automate on-demand loading of ion qubit chains, and can carry out simple qubit manipulations using microwave fields. The team is making great progress towards implementing entangling gates, in a way that can support up to full 32 qubits.

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