Quantum computers promise large-scale data processing in future commercial and military communications networks, once some of the limitations of the technology and available communications bandwidth are overcome. In contrast to the standard “1” and “0” electron bits of conventional computers, quantum computers are based on qubits formed with photons and light and capable of processing much more data than standard computers. But hardware has been limited because of the optical speeds of components required. However, a method revealed by engineers from Purdue University in the journal Optica promises large amounts of data to many users over quantum computer optical networks, enabling the use of quantum computers in data-intensive applications such as radar systems and high-speed encrypted communications networks such as a quantum internet.
The method uses a high-speed switch as a filter (see figure), controlling how much data is transferred to each user on a network by switching among different data channels on optical channels. By selecting among optical wavelengths rather than sending a wide spectrum, bandwidth can be conserved and photons (and their corresponding data) will not be lost in a quantum network. Andrew Weiner, Purdue’s Scifres Family Distinguished Professor of Electrical and Computer Engineering, explained: “We show a way to do wavelength routing with just one piece of equipment—a wavelength-selective switch—to, in principle, build a network of 12 to 20 users, maybe even more.” The wavelength-selective switch can be programmed to adjust bandwidth according to a user’s needs so that spectrum is used efficiently. Fixed optical filters currently used for this purpose lack the programmability.
The research was performed in collaboration with Joseph Lukens, a research scientist at Oak Ridge National Laboratory (ORNL). The switch can be used to create a flex grid based on wavelength division multiplexing (WDM), in which bandwidth is partitioned to users at many different wavelengths and portions of the optical spectrum rather than in a series of fixed wavelengths and bandwidths, emulating classical communications concepts. The research team hopes to build larger quantum networks with the optical switch. The work is being funded by the U. S. Department of Energy (DoE), the National Science Foundation (NSF), and ORNL.