The image shows the crystal disk containing erbium atoms in the middle. Meanwhile, the red disks represent the light reflecting back and forth (Image Credit: Christoph Hohmann (MCQST))

The first quantum revolution introduced semiconductor electronics, the laser, and the internet. Now, the second quantum revolution expects to bring spy-proof communication, very precise quantum sensors, and quantum computers for previously unsolvable computing tasks.   Physicists at the Max-Planck-Institute of Quantum Optics in Garching have developed simple and highly efficient technology for a "quantum modem" integrated into fiber-optic networks. This could allow users to connect to a quantum internet in the future.


"In the future, a quantum internet could be used to connect quantum computers located in different places," says physicist Andreas Reiserer, "which would considerably increase their computing power!"


This newly-developed system is designed to establish a connection between flying and stationary qubits. The team developed new technology and demonstrated its functionality. Its main advantage is that it could be incorporated into the existing telecommunications fiber-optic network. This makes it the quickest way to advance long-distance networking of quantum technologies.


The quantum modem works by using light photons to store quantum information being sent or received. These are precisely matched to the infrared wavelength of laser light used in today's telecommunications. This means the modem has qubits at rest that react precisely to the infrared photons with a quantum leap. That way, the sensitive quantum information can be transmitted between the resting qubits and the flying qubits.


For this purpose, the team used erbium atoms as stationary qubits. Their electrons are capable of making a quantum leap that matches the infrared wavelength of the photons in the fiber optic networks. However, the photons must force the erbium atoms to react so they could make the quantum leap.  The team accomplished this by packing the atoms into a transparent crystal comprised of a yttrium silicate compound five times thinner than a human hair.


The outside of the mirror cabinet is shown here. It can establish a connection between flying and stationary qubits. (Image Credit: Christoph Hohmann (MCQST))


In turn, this crystal was inserted between a mini mirrored cabinet. To prevent the heat wobbling of the atoms, which causes damage to quantum information, the team cooled the system down to -271 °C (-455.8 °F). In the mirror cabinet, the photons are reflected back and forth, passing the erbium atoms so frequently that it causes them to react and make a quantum leap. This happens much more efficiently and nearly sixty times faster than without the mirror cabinet. The modem can connect to the network since the mirrors are also somewhat permeable to photons.


"We are very happy about this success," Reiserer says. Next, the team wants to improve the experiment so that single erbium atoms can be addressed as qubits via laser light. Erbium atoms as qubits in a crystal could function as a quantum processor, making the modem compatible with quantum terminals. The quantum modem is still fundamental research, but it could pave the way towards a quantum internet.


This image shows a close-up image of an array pillar, which works as a location marker for a quantum state that interacts with photons.  (Image Credit: University of Rochester illustration / Michael Osadciw)


Researchers at the University of Rochester and Cornell University have designed a nanoscale node comprised of magnetic and semiconducting materials that could interact with other nodes. It uses laser light to discharge and accept photons.


The node contains an array of pillars that are 120 nanometers high. The pillars are part of a platform consisting of atomically thin layers of semiconductors and magnetic materials. The array is designed so that each pillar works as a location marker for a quantum state that interacts with photons, and the corresponding photons can interact with other locations across the device.


This newly-developed device utilizes a unique alignment of tungsten diselenide (WSe2) covered over the pillars with an extremely reactive layer of chromium triiodide (CrI3). Where the 12-micron area layers touch, the Crl13 discharges an electric charge to the WSe2, which produces a hole alongside each pillar.


More reactions occur when the device is blanketed in laser light, which transforms the nanomagnets into individual optically active spin arrays that emit and interact with photons. Spin states could potentially extend the possibilities for information processing since it simultaneously encodes bits with values of zero and one.


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