US Army researchers have affirmed that future quantum computer circuits will not require extremely cold temperatures to function and it could become a reality as early as a decade.
In a quantum computer, the basic unit of memory is a quantum bit or qubit while classical computers—like laptops and smart phones —encode information in binary bits that can either be 0s or 1s. Therefore, they have the potential to process exponentially more data compared to classical computers which mean quantum computer could vastly outperform even our best supercomputers.
One of the major drawbacks of quantum systems is the fragility of the strange states of the qubits (or quantum bit, the basic unit of quantum information). Most prospective hardware for quantum technology must be kept at extremely cold temperatures—close to zero kelvins—to prevent the special states being destroyed by interacting with the computer's environment.
Scientists in many countries have been working to build stable qubits (or quantum bit, the basic unit of quantum information) that operate at room temperatures. Quantum technology offers a range of future advances in computing, communications and remote sensing.
For years, solid-state quantum technology that operates at room temperature seemed remote. While the application of transparent crystals with optical nonlinearities had emerged as the most likely route to this milestone, the plausibility of such a system always remained in question.
Army scientists have officially confirmed the validity of this approach. Dr. Kurt Jacobs, of the US Army Combat Capabilities Development Command's Army Research Laboratory, working alongside Dr. Mikkel Heuck and Prof. Dirk Englund, of the Massachusetts Institute of Technology, became the first to demonstrate the feasibility of a quantum logic gate comprised of photonic circuits and optical crystals.
"If future devices that use quantum technologies will require cooling to very cold temperatures, then this will make them expensive, bulky, and power hungry," Heuck said. "Our research is aimed at developing future photonic circuits that will be able to manipulate the entanglement required for quantum devices at room temperature."
"Any interaction that a qubit has with anything else in its environment will start to distort its quantum state," Jacobs said.
Unlike quantum systems that use ions or atoms to store information, quantum systems that use photons can bypass the cold temperature limitation. However, the photons must still interact with other photons to perform logic operations. This is where the nonlinear optical crystals come into play.
Researchers can engineer cavities in the crystals that temporarily trap photons inside. Through this method, the quantum system can establish two different possible states that a qubit can hold: a cavity with a photon (on) and a cavity without a photon (off). These qubits can then form quantum logic gates, which create the framework for the strange states.
In other words, researchers can use the indeterminate state of whether or not a photon is in a crystal cavity to represent a qubit. The logic gates act on two qubits together, and can create "quantum entanglement" between them. This entanglement is automatically generated in a quantum computer, and is required for quantum approaches to applications in sensing.
Once they designed the quantum logic gate, the researchers performed numerous computer simulations of the operation of the gate to demonstrate that it could, in theory, function appropriately. Actual construction of a quantum logic gate with this method will first require significant improvements in the quality of certain photonic components, researchers said.
"Based on the progress made over the last decade, we expect that it will take about ten years for the necessary improvements to be realized," Heuck said.
Physical Review Letters published the team's findings in a peer-reviewed paper on April 20.