Scientists have gotten one step closer to a quantum internet by creating the world’s first multinode quantum network.
Researchers at the QuTech research centre in Netherlands created the system, which is formed from three quantum nodes entangled by the spooky laws of quantum physics that govern subatomic particles. it’s the first time that more than two quantum bits, or “qubits,” that do the calculations in quantum computing are linked together as “nodes,” or network endpoints.
Researchers expect the first quantum networks to unlock a wealth of computing applications that can’t be performed by existing classical devices — like faster computation and improved cryptography.
“It will allow us to attach quantum computers for more computing power, create unhackable networks and connect atomic clocks and telescopes along side unprecedented levels of coordination,” Matteo Pompili, a member of the QuTech research team that created the network at Delft University of Technology in Netherlands, told Live Science. “There also are a lot of applications that we can’t really foresee. One might be to create an algorithm which will run elections in secure way, as an example .”
In much same way that the normal computer bit is that the basic unit of digital information, the qubit is that the basic unit of quantum information. Just like the bit, the qubit are often either a 1 or a 0, which represent 2 possible positions during a two-state system.
But that’s almost where the similarities end. Because of the bizarre laws of the quantum world, the qubit can exist during a superposition of both the 1 and 0 states until the instant it’s measured, when it’ll randomly collapse into either a 1 or a 0. This strange behavior is that the key to the power of quantum computing, because it allows a qubit to perform multiple calculations simultaneously.
The biggest challenge in linking those qubits together into a quantum network is in establishing and maintaining a process called entanglement, or what Einstein dubbed “spooky action at a distance.” this is often when two qubits become coupled, linking their properties in order that any change in one particle will cause a change in other, even they’re separated by vast distances.
You can entangle quantum nodes during a lot of the way , but one common method works by first entangling the stationary qubits (which form the network’s nodes) with photons, or light particles, before firing the photons at one another . once they meet, the 2 photons also become entangled, thereby entangling the qubits. This binds the 2 stationary nodes that are separated by a distance. Any change made to at least one is reflected by an instant change to other.
“Spooky action at a distance” lets scientists change the state of a particle by altering the state of its distant entangled partner, effectively teleporting information across big gaps. But maintaining a state of entanglement may be a tough task, especially because the entangled system is usually in danger of interacting with the outside world and being destroyed by a process called decoherence.
This means, first, that the quantum nodes need to be kept at extremely cold temperatures inside devices called cryostats to minimize the probabilities that the qubits will interfere with something outside the system. Second, the photons utilized in the entanglement can’t travel very long distances before they’re absorbed or scattered, — destroying the signal being sent between two nodes.
“The problem is, unlike classical networks, you can’t amplify quantum signals. If you are trying to copy the qubit, you destroy the first copy,” Pompili said, referring to physics’ “no-cloning theorem,” which states that it’s impossible to make a identical copy of an unknown quantum state. “This really limits the distances we can send quantum signals to the tens of hundreds kilometers. If you would like to line up quantum communication with someone on the opposite side of the world, you’ll need relay nodes in between.”
To solve the matter, the team created a network with three nodes, during which photons essentially “pass” the entanglement from a qubit at one among the outer nodes to at least one at the middle node. The middle node has two qubits — one to acquire an entangled state and one to store it. Once the entanglement between one outer node and therefore the middle node is stored, the middle node entangles the opposite outer node with its spare qubit. With all of this done, the middle node entangles its two qubits, causing the qubits of the outer nodes to become entangled.
But designing this weird quantum mechanical spin on the classic “river crossing puzzle” was the smallest amount of the researchers troubles — weird, for sure, but not too tricky a idea. To form the entangled photons and beam them to the nodes in right way, the researchers had to use a complex system of mirrors and laser light. The really tough part was the technological challenge of reducing pesky noise in system, also as ensuring all of the lasers used to produce the photons were perfectly synchronized.
“We’re talking about having 3-4 lasers for each node, so you begin to possess 10 lasers and three cryostats that each one have to work on same time, along side all of the electronics and synchronization,” Pompili said.
The three-node system is especially useful because the memory qubit allows researchers to establish entanglement across the network node by node, instead of the more demanding requirement of doing it all at once. As soon as this is often done, information are often beamed across the network.
Some of the researchers next steps with their new network are going to attempt this information beaming, along with improving essential components of the network’s computing abilities in order that they will work like regular computer networks do. All of those things will set the size that the new quantum network could reach.
They also want to see if their system will allow them to establish entanglement b/w Delft and therefore the Hague, two Dutch cities that are roughly 6 miles (10 kilometers) apart.
“Right now, all of our nodes are within 10-20 meters [32- 66 feet] of each-other,” Pompili said. “If you would like something useful, you would like to travel to kilometers. This is often getting to be the first time that we’re getting to make a link between long distances.”
The researchers published their findings April 16 in the journal Science.