The emerging quantum revolution offer revolutionary capabilities for military from quantum creptography for hack proof communications to High-precision atomic clocks that can enable timekeeping for navigation and communications with GPS-like performance even in GPS-denied environments. Another important area is quantum computing based on quantum bits, or qubits, which can represent a one, a zero, or a coherent linear combination of one and zero, could open routes to new kinds of computation.
Quantum sensors are measuring device that takes advantage of quantum correlations, such as states in a quantum superposition or entanglement, for better sensitivity and resolution than can be obtained by classical systems. The performance and reliability of quantum sensors and devices is dependent on the length of time the underlying quantum states can remain coherent.
However, existing quantum devices are extremely fragile and sensitive to environment, and even in short time interaction with the environment make them lose their quantum behavior. States of quantum coherence are relatively short-lived because quantum particles are extremely sensitive to their surroundings and quickly become unstable, losing their predictable and readily measurable quantum properties due to even the slightest thermal variation or other disturbance in the environment.
DARPA’s Defense Sciences Office (DSO) announced in Jan a new fundamental research program, Driven and Nonequilibrium Quantum Systems (DRINQS) to investigate a recent paradigm shift in quantum research, which maintains that periodically driving a system out of equilibrium may stabilize its coherence.
“Atoms and subatomic particles in a quantum state do not always get along well with other particles and currently need special isolated environments where no thermal, electromagnetic, or other disturbance will cause them to lose their coherence,” Lukaszew said. “That’s why the world’s best atomic clocks for precision timing, which DARPA is pioneering in other programs, require special laboratory environments for isolating individual atoms from each other. This involves slowing atoms down by cooling them to near absolute zero temperature and creating with lasers a lattice structure in which the chilled atoms can rest quietly, unperturbed by their neighbors like eggs in a carton.”
“A simple illustration of the concept of driving something out of equilibrium to increase its stability is the well-known trick of making an inverted broom stand up on the palm of your hand or on one of your fingertips,” said Ale Lukaszew, DARPA program manager. “If you hold your hand still, the broom is unstable and will fall over quickly. But if you drive the broom out of equilibrium by moving your hand around periodically, you can make the broom very stable, so it remains upright indefinitely.”
“If we can introduce a periodic drive to enable particles to be packaged close together in small spaces at room temperature, while still retaining quantum coherence, we may be able to reproduce the performance of the best sensors, such as atomic clocks and magnetometers, in small and robust devices for military use,” Lukaszew said.
The new program will build collaborative teams of theoreticians and experimentalists to address novel approaches for driving quantum systems made up of large numbers of particles. The teams will be tasked to develop novel protocols for stabilizing coherence in a driven system and demonstrate proof-of-principle concepts that achieve at least 10-fold, and possibly 100-fold, improvement over the standard limits of quantum coherence.
“One exciting potential application for extremely precise atomic-based time measurements is measuring gravitational fields, which could be very useful in tunnel and cave detection,” Lukaszew said. “In principle, existing atomic-clocks can keep time precisely enough to measure gravitational field differences over the distance of a few feet, but it could take weeks to process the measurement. If we can engineer a system that doesn’t lose its coherence as fast and can be re-tuned very quickly, we could potentially make those same measurements in half an hour.
Driven and Nonequilibrium Quantum Systems (DRINQS) program
The performance of quantum sensors and devices is intimately dependent on the time the underlying system retains its quantum properties, namely its coherence time, T2. Interactions within the system and with a noisy environment are typically the limiting factors of T2; therefore, the best devices require extremely clean control signals and cryogenic operation to reduce thermal noise. This has limited the applicability and adoption of quantum technology in various applications of interest to national security, including high performance clocks for holdover in GPS-denied environment and magnetometers for magnetic navigation and life-science imaging.
Over the last couple of years, a new paradigm for overcoming the limitations of coherence in large-scale quantum systems has been proposed: the coherence of a system may be stabilized by driving it out of equilibrium.
One example of this phenomenon is a discrete time crystal (DTC). In this driven system, a combination of interactions and disorder force the system into a state in which it thermalizes at a much lower rate than when not driven. In addition, the system exhibits an increased resilience against perturbations in the drive than in the absence of interactions and disorder.
This phenomenon has recently been experimentally observed with trapped ions and Nitrogen-Vacancy (NV) color centers in diamond. Another example is the stabilization of coherence in quantum materials when driven with strong electromagnetic fields, such as the inducement of superconductivity at high temperatures using laser pulses, albeit for a short period of time. Novel non-equilibrium phases may be produced by selectively exciting phonons thus changing the structural and electronic properties of the material in a controlled way
DRINQS is a fundamental science program that seeks to validate that the improvements in coherence seen in driven systems can be exploited for applications of interest to national security. The program aims to demonstrate that significant gains over conventional state of practice can be obtained in timekeeping, field sensing and quantum information processing using these techniques. By the end of the program, the following goals should be achieved:
- A determination and experimental demonstration of what protocols can optimally enhance quantum coherence in driven systems.
- Proof-of-principle demonstrations of 10X improvement over the use of conventional techniques in clock stability, high spatial resolution field sensing and quantum information applications.