Quantum Science

As part of the then three-year-old Quantum Information Science and Technology (QuIST) program, DARPA-funded researchers established the first so-called quantum key distribution network, which is a data encryption framework for protecting a fiber-optic loop that connects facilities at Harvard University, Boston University, and the office of BBN Technologies in Cambridge, Mass.

In science, many of the most interesting events occur at a scale far smaller than the unaided human eye can see. Medical researchers might realize a range of breakthroughs if they could look deep inside living biological cells, but existing methods for imaging either lack the desired sensitivity and resolution or require conditions that lead to cell death, such as cryogenic temperatures. Recently, however, a team of Harvard University-led researchers working on DARPA’s Quantum-Assisted Sensing and Readout (QuASAR) program demonstrated imaging of magnetic structures inside of living cells.

How do you take the temperature of a cell? The familiar thermometer from a doctor’s office is slightly too big considering the average human skin cell is only 30 millionths of a meter wide. But the capability is significant; developing the right technology to gauge and control the internal temperatures of cells and other nanospaces might open the door to a number of defense and medical applications: better thermal management of electronics, monitoring the structural integrity of high-performance materials, cell-specific treatment of disease and new tools for medical research.

Researchers from the National Institute of Standards and Technology (NIST), with funding from DARPA’s Quantum-Assisted Sensing and Readout (QuASAR) program, have built a pair of ytterbium atomic clocks that measure time with a precision that is approximately ten times better than the world’s previous best clocks, also developed under QuASAR. How good are they? The record-setting clocks are stable to within less than two parts per quintillion (1 followed by 18 zeros). They measure time so precisely that their readout would be equivalent to specifying the Earth’s diameter to less than the width of a single atom or the age of the known universe to less than one second.

Microelectromechanical systems, known as MEMS, are ubiquitous in modern military systems such as gyroscopes for navigation, tiny microphones for lightweight radios, and medical biosensors for assessing the wounded. Such applications benefit from the portability, low power, and low cost of MEMS devices. Although the use of MEMS sensors is now commonplace, they still operate many orders of magnitude below their theoretical performance limits. This is due to two obstacles: thermal fluctuations and random quantum fluctuations, a barrier known as the standard quantum limit.