Innovative System can Help Develop Practical Quantum Computers

In a first-of-its-kind study, scientists have successfully developed a 32-qubit trapped-ion quantum computer register that works even at cryogenic temperatures.

The latest, fully connected system brings scientists one step closer to designing practical quantum computers.

This novel hardware design will be presented at the inaugural OSA Quantum 2.0 conference by Junki Kim from Duke University. The conference will be jointly located as an all-virtual event with OSA Frontiers in Optics and Laser Science APS/DLS (FiO + LS) conference from September 14th to 17th, 2020.

Quantum computers typically employ qubits rather than using conventional computer bits that can only be a one or a zero. These qubits can remain in a superposition of computational states. It is this feature that enables quantum computers to solve issues that prove too complicated for conventional computers.

One of the most potential types of quantum technology for quantum computing is trapped-ion quantum computers; however, scientists have found it difficult to develop such computers that have sufficient qubits for practical applications.

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

Junki Kim, Duke University

Scaling up Quantum Computers

Trapped-ion quantum computers are capable of cooling ions to very low temperatures, enabling them to be suspended in an electromagnetic field in an extremely high vacuum and subsequently exploited with accurate lasers to create qubits.

To date, scientists have found it challenging to achieve high computational performance in the case of large-scale ion trap systems. These limitations can be attributed to the instability of the laser beams powering the logic gates identified by the ion, the collisions with background molecules disturbing the chain of ions, and the electric field noise that results from the trapping electrodes agitating the movement of the ion often used for producing the entanglement.

To deal with these challenges, Kim and collaborators incorporated radically new methods in the latest study. The ions are initially confined to a localized ultra-high vacuum enclosure within a closed-cycle cryostat—cooled to 4 K temperatures—with the least vibrations. This set up prevents the disruption of the qubit chain caused by collisions with remaining molecules from the setting and robustly inhibits the anomalous heating from the trap surface.

To reduce errors and simultaneously realize clean laser beam profiles, a photonic crystal fiber was used to link numerous parts of the Raman optical system driving the qubit gates—that is, the building blocks of quantum circuits.

Moreover, the fragile laser systems required to use the quantum computers are designed such that they can be removed from the optical table and embedded in instrument racks. Following this, the laser beams are sent to the system in single-mode optical fibers.

The team adopted innovative ways of developing and applying optical systems that basically prevent thermal and mechanical instabilities to produce a turn-key laser arrangement with regard to trapped ion quantum computers.

The team has further shown that the system can perform automated on-demand loading of ion qubit chains, and can even execute easy qubit manipulations through microwave fields. The researchers are making rapid advancements to implement entangling gates, in a way that can scale up to full 32 qubits.

In upcoming studies, and in association with quantum algorithm scientists and computer scientists, the researchers have planned to incorporate the trapped-ion quantum computing hardware with hardware-specific software.

Integrated with hardware-specific software and fully connected trapped-ion qubits, the fully integrated quantum system will set a new benchmark for hands-on trapped-ion quantum computers.

The study is part of a multi-institutional NSF-funded Software-Tailored Architecture for Quantum co-design (STAQ) project headed by Kenneth Brown at Duke University.


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