Researchers at the U.S. Army Research Laboratory recently achieved a major milestone for the lab’s efforts in quantum information and computation.
Physicist Dr. Qudsia Quraishi, who works in the lab’s Sensors and Electron Devices Directorate, and University of Maryland postdoctoral researcher Dr. James Siverns and graduate student John Hannegan are the first researchers to trap ions for ARL.
According to Quraishi, trapped ions are a strong contender for quantum information and quantum computation, and have promising potential for future Army applications.
“The Army has a vested interest in quantum information and quantum computation as it has potential application for data storage, tactical advantages for quantum-based frequency and timing synchronization, quantum-based communication for eaves-drop free communication and protection of modern data encryption,” Quraishi said.
ARL has a new mission program in quantum networking, which Quraishi helped to set up, and is recognized as taking a leadership role in this area.
“We want to leverage advances made in trapped ion research for Army-specific aims and so our mission work involves networking remotely situated ions together using quantum entanglement,” Quraishi said. “Trapping an ion is the necessary first step in building the first such node at ARL.”
Quraishi noted quantum information with atomic ions involves trapping a relatively small number of ions, typically from one to ten.
“Although recent experiments have trapped upwards of 50 ions, most of the trapped ion community works with just a handful of ions,” Quraishi said.
Assembling the trap
To trap ions, one needs three main components, a small custom designed electrode structure placed inside an ultra-high vacuum chamber, use of established radio frequency technology, and a set of referenced and stabilized lasers resonant with the ion’s internal transitions.
“Most of the effort is in the design and assembly of the trap electrode structure and in placing and testing this trap in a custom ultra-high vacuum chamber,” Quraishi said.
ARL’s trap, assembled by the researchers by hand, consists of 12 separate electrodes, and is called a blade trap.
This trap consists of four gold coated alumina blades arranged in an “X” pattern with around 100-200 micrometer gaps between each blade tip. After the trap is assembled, it is placed inside a vacuum chamber. The vacuum is approximately 14 orders of magnitude lower in pressure than atmospheric pressure.
According to Quraishi, care must be taken to avoid any contamination such as dust or finger prints on the trap electrodes or interior parts of the vacuum chamber.
“To achieve this, each part of the vacuum system was sent through a thorough cleaning procedure, which included rinsing in high purity methanol and ultrasonic cleaning, as well as pre-baking for several days at over 200 degrees Celsius,” Quraishi said.
Once the vacuum chamber was fully assembled with the trap inside, it was baked at 180 degrees Celsius for two weeks to remove any remaining impurities in the system to allow it to reach ultra-high vacuum pressures.
“Any collision of the trapped ion with background gas particles could destroy quantum states mapped onto the ion, or even kick the ion out of the trap minimum, so the lower the final pressure achieved, the better the experiment will perform,” Quraishi said.
Trapping the ions
The electric fields for trapping the ions are generated by applying a radio-frequency (about 30 megahertz) voltage of 600 V to two of the electrodes, producing a time-averaged force on the ion keeping it confined to the center of the trapping region.
The researchers used lasers that have minimal noise and are locked to a neutral atom reference to prevent their frequencies from drifting more than one to two megahertz over the course of a day.
The researchers have trapped Ba+ and Yb+ ions and have observed good trap stability and lifetimes of hours.
This research was conducted via ARL’s Center for Distributed Quantum Information, which is a collaborative basic research effort connecting ARL, academic, industrial and other government researchers to develop a multi-site, multi-node, modular quantum network based on resilient distributed quantum entanglement preserved by quantum memory and quantum error correction.
Specifically, the project was conducted on site at the University of Maryland, College Park, an academic partner involved in the Center for Distributed Quantum Information, at the Open Campus joint ARL/Joint Quantum Institute Lab.
The U.S. Army Research Laboratory, currently celebrating 25 years of excellence in Army science and technology, is part of the U.S. Army Research, Development and Engineering Command, which has the mission to provide innovative research, development and engineering to produce capabilities that provide decisive overmatch to the Army against the complexities of the current and future operating environments in support of the joint warfighter and the nation. RDECOM is a major subordinate command of the U.S. Army Materiel Command.
By Jenna Brady, U.S. Army Research Laboratory