quantum dots

Researchers at JQI and the National Institute of Standards and Technology (NIST) have developed standards and calibrations for optical microscopes that allow quantum dots to be aligned with the center of a photonic component to within an error of 10 to 20 nanometers (about one-thousandth the thickness of a sheet of paper). Such alignment is critical for chip-scale devices that employ the radiation emitted by quantum dots to store and transmit quantum information.

Quantum behavior plays a crucial role in novel and emergent material properties, such as superconductivity and magnetism. Unfortunately, it is still impossible to calculate the underlying quantum behavior, let alone fully understand it. Scientists of QuTech, the Kavli Institute of Nanoscience in Delft and TNO, in collaboration with ETH Zurich and the University of Maryland, have now succeeded in building an "artificial material" that mimics this type of quantum behavior on a small scale. In doing so, they have laid the foundations for new insights and potential applications. Their work is published today in Nature.

From credit card numbers to bank account information, we transmit sensitive digital information over the internet every day. Since the 1990s, though, researchers have known that quantum computers threaten to disrupt the security of these transactions. That’s because quantum physics predicts that these computers could do some calculations far faster than their conventional counterparts. This would let a quantum computer crack a common internet security system called public key cryptography. This system lets two computers establish private connections hidden from potential hackers. In public key cryptography, every device hands out copies of its own public key, which is a piece of digital information.  Any other device can use that public key to scramble a message and send it back to the first device. The first device is the only one that has another piece of information, its private key, which it uses to decrypt the message. Two computers can use this method to create a secure channel and send information back and forth. A quantum computer could quickly calculate another device’s private key and read its messages, putting every future communication at risk. But many scientists are studying how quantum physics can fight back and help create safer communication lines.

Today’s networks use electronic circuits to store information and optical fibers to carry it, and quantum networks may benefit from a similar framework. Such networks would transmit qubits – quantum versions of ordinary bits – from place to place and would offer unbreakable security for the transmitted information. But researchers must first develop ways for qubits that are better at storing information to interact with individual packets of light called photons that are better at transporting it, a task achieved in conventional networks by electro-optic modulators that use electronic signals to modulate properties of light. Now, researchers in the group of Edo Waks have struck upon an interface between photons and single electrons that makes progress toward such a device.

A collaboration between JQI and Princeton University researchers has resulted in a rice grain-sized laser powered by single electrons tunneling through artificial atoms known as quantum dots. The tiny microwave laser, or "maser," is a demonstration of the fundamental interactions between light and moving electrons.

The researchers built the device — which uses about one-billionth the electric current needed to power a hair dryer — while exploring how to use quantum dots, which are bits of semiconductor material that act like single atoms, as components for quantum computers.

Encoding information using quantum bits—which can be maintained in a superposition of states—is at the heart of quantum computing. Superposition states offer the advantage of massive parallelism compared to conventional computing using digital bits---which can assume only one value at a time.  

What will a quantum computer look like? It will probably not resemble your laptop.  Yet, the semiconductor industry, residing at the heart of modern computing, has features that may carry over. Semiconductors are scalable: today’s processors (2.5 centimeters on a side) hold billions of transistors. Another benefit: semiconductor technology integrates with existing electronic and photonic elements. These practical considerations have led some researchers to construct semiconductor quantum devices. 

If you could peek at the inner workings of a computer processor you would see billions of transistors switching back and forth between two states. In optical communications, information from the switches can be encoded onto light, which then travels long distances through glass fiber. Researchers at the Joint Quantum Institute and the Department of Electrical and Computer Engineering are working to harness the quantum nature of light and semiconductors to expand the capabilities of computers in remarkable ways.

An optical switch developed at the Joint Quantum Institute (JQI) spurs the prospective integration of photonics and electronics. What, isn’t electronics good enough? Well, nothing travels faster than light, and in the effort to speed up the processing and transmission of information, the combined use of light parcels (photons) along with electricity parcels (electrons) is desirable for developing a workable opto-electronic protocol.