System Bits: Oct. 28

Sensing objects without looking at them
In a technique known as “interaction-free measurement,” Yale engineers have created a chip-scale device that senses the presence of an object without interacting with it by using the wave-particle duality of single photons. This work could help propel the field of quantum information processing.

The researchers explained that the device uses silicon photonics to create interaction-free measurement on an IC, which is something only previously accomplished on the much larger scale of traditional bulk optics.

They explained that the device utilizes a single photon’s ability to exhibit the properties of both a particle and a wave. This is a central concept of quantum mechanics known as wave-particle duality that recognizes that quantum particles exhibit continuous wave-like movement through space, yet can paradoxically also occupy a definable specific location, like a particle.

In an interaction-free measurement, quantum particles could take one of the two distinct paths in an interferometer or both. However, if an object is placed on one of those paths, the quantum particles will choose a different path to avoid interaction with the object with certain probability.

“It seems a counterintuitive phenomena, but the quantum particle avoids the object without interacting with it, essentially sensing the object without looking at it,” said Xiao-Song Ma, lead author of the study. “Our device takes advantage of this behavior by recognizing when a path is being avoided, allowing us to also sense the presence of the object without any interaction.”

The researchers stressed that integrated photonics is a promising approach to realizing quantum information processing, and that devices such as theirs this will realize the promise to improve communication security as well as speed-up certain types of computing.

Precise, programmable bio circuits
A team of ETH researchers has developed several new components for biological circuits, which are key building blocks for constructing precisely functioning and programmable bio-computers.

ETH researchers and other bio-engineers are working on the development of biological computers with the aim of designing small circuits made from biological material that can be integrated into cells to change their functions. Such developments could enable cancer cells to be reprogrammed, thereby preventing them from dividing at an uncontrollable rate; or could allow stem cells to be reprogrammed into differentiated organ cells.

While the researchers have not progressed that far yet, they’ve spent the past 20 years developing individual components and prototypes of biological computers, but bio-computers today still differ significantly from their counterparts made of silicon. At the same time, bio-engineers face several major obstacles.

The researchers reminded that a silicon chip, for example, computes with ones and zeros – current is either flowing or not – and it can switch between these states in the blink of an eye. In contrast, biological signals are less clear: in addition to ‘signal’ and ‘no signal’, there is a plethora of intermediate states with ‘a little bit of signal’. This is a particular disadvantage for bio-computer components that serve as sensors for specific biomolecules and transmit the relevant signal. Sometimes, they also send an output signal if no input signal is present, and the problem becomes worse when several such components are connected consecutively in a circuit.

Now, the team has developed a biological circuit that controls the activity of individual sensor components using an internal “timer,” which prevents a sensor from being active when not required by the system. When required, it can be activated via a control signal.

The researchers expect this new biological platform to greatly increase the number of applications for biological circuits. The team lead added that the ability to combine biological components at will in a modular, plug-and-play fashion means that we now approach the stage when the concept of programming as we know it from software engineering can be applied to biological computers. Bio-engineers will literally be able to program in future.