Larian's Baldur's Gate 3 leads the 2024 BAFTA Games Awards with 10 nominations, including Best Game, as it celebrates its 20th anniversary this year.

BAFTA today released the shortlist of nominees for this year's awards, with Marvel's Spider-Man 2 receiving nine nominations, Alan Wake 2 receiving eight nominations, and The Legend of Zelda: Tears of the Kingdom and Star Wars Jedi: Survivor both receiving six.

The coveted Best Game will be awarded to either Alan Wake 2, Baldur's Gate 3, Dave the Diver, The Legend of Zelda: Tears of the Kingdom, Marvel's Spider-Man 2, or Super Mario Bros. Wonder.

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The popular children's game of telephone is based on a simple premise: The starting player whispers a message into the ear of the next player. That second player then passes along the message to the third person and so on until the message reaches the final recipient, who relays it to the group aloud. Often, what the first person said and the last person heard are laughably different; the information gets garbled along the chain.

Such transmission errors from start to end point are also common in the quantum world. As quantum information bits, or qubits (the analogs of classical bits in traditional digital electronics), make their way over a channel, their quantum states can degrade or be lost entirely. Such decoherence is especially common over longer and longer distances because qubits — whether existing as particles of light (photons), electrons, atoms, or other forms — are inherently fragile, governed by the laws of quantum physics, or the physics of very small objects. At this tiny scale (nanoscale), even slight interactions with their environment can cause qubits to lose their quantum properties and alter the information they store. Like the game of telephone, the original and received messages may not be the same.

"One of the big challenges in quantum networking is how to effectively move these delicate quantum states between multiple quantum systems," says Scott Hamilton, leader of MIT Lincoln Laboratory's Optical and Quantum Communications Technology Group, part of the Communications Systems R&D area. "That's a question we're actively exploring in our group."

As Hamilton explains, today's quantum computing chips contain on the order of 100 qubits. But thousands, if not billions, of qubits are required to make a fully functioning quantum computer, which promises to unlock unprecedented computational power for applications ranging from artificial intelligence and cybersecurity to health care and manufacturing. Interconnecting the chips to make one big computer may provide a viable path forward. On the sensing front, connecting quantum sensors to share quantum information may enable new capabilities and performance gains beyond those of an individual sensor. For example, a shared quantum reference between multiple sensors could be used to more precisely locate radio-frequency emission sources. Space and defense agencies are also interested in interconnecting quantum sensors separated by long ranges for satellite-based position, navigation, and timing systems or atomic clock networks between satellites. For communications, quantum satellites could be used as part of a quantum network architecture connecting local ground-based stations, creating a truly global quantum internet.

However, quantum systems can't be interconnected with existing technology. The communication systems used today to transmit information across a network and connect devices rely on detectors that measure bits and amplifiers that copy bits. These technologies do not work in a quantum network because qubits cannot be measured or copied without destroying the quantum state; qubits exist in a superposition of states between zero and one, as opposed to classical bits, which are in a set state of either zero (off) or one (on). Therefore, researchers have been trying to develop the quantum equivalents of classical amplifiers to overcome transmission and interconnection loss. These equivalents are known as quantum repeaters, and they work similarly in concept to amplifiers, dividing the transmission distance into smaller, more manageable segments to lessen losses.

"Quantum repeaters are a critical technology for quantum networks to successfully send information over lossy links," Hamilton says. "But nobody has made a fully functional quantum repeater yet."

The complexity lies in how quantum repeaters operate. Rather than employing a simple "copy and paste," as classical repeaters do, quantum repeaters work by leveraging a strange quantum phenomenon called entanglement. In quantum entanglement, two particles become strongly connected and correlated across space, no matter the distance between them. If you know the state of one particle in an entangled pair, then you automatically know the state of the other. Entangled qubits can serve as a resource for quantum teleportation, in which quantum information is sent between distant systems without moving actual particles; the information vanishes at one location and reappears at another. Teleportation skips the physical journey along fiber-optic cables and therefore eliminates the associated risk of information loss. Quantum repeaters are what tie everything together: they enable the end-to-end generation of quantum entanglement, and, ultimately, with quantum teleportation, the end-to-end transmission of qubits.

Ben Dixon, a researcher in the Optical and Quantum Communications Technology Group, explains how the process works: "First, you need to generate pairs of specific entangled qubits (called Bell states) and transmit them in different directions across the network link to two separate quantum repeaters, which capture and store these qubits. One of the quantum repeaters then does a two-qubit measurement between the transmitted and stored qubit and an arbitrary qubit that we want to send across the link in order to interconnect the remote quantum systems. The measurement results are communicated to the quantum repeater at the other end of the link; the repeater uses these results to turn the stored Bell state qubit into the arbitrary qubit. Lastly, the repeater can send the arbitrary qubit into the quantum system, thereby linking the two remote quantum systems."

To retain the entangled states, the quantum repeater needs a way to store them — in essence, a memory. In 2020, collaborators at Harvard University demonstrated holding a qubit in a single silicon atom (trapped between two empty spaces left behind by removing two carbon atoms) in diamond. This silicon "vacancy" center in diamond is an attractive quantum memory option. Like other individual electrons, the outermost (valence) electron on the silicon atom can point either up or down, similar to a bar magnet with north and south poles. The direction that the electron points is known as its spin, and the two possible spin states, spin up or spin down, are akin to the ones and zeros used by computers to represent, process, and store information. Moreover, silicon's valence electron can be manipulated with visible light to transfer and store a photonic qubit in the electron spin state. The Harvard researchers did exactly this; they patterned an optical waveguide (a structure that guides light in a desired direction) surrounded by a nanophotonic optical cavity to have a photon strongly interact with the silicon atom and impart its quantum state onto that atom. Collaborators at MIT then showed this basic functionality could work with multiple waveguides; they patterned eight waveguides and successfully generated silicon vacancies inside them all. 

Lincoln Laboratory has since been applying quantum engineering to create a quantum memory module equipped with additional capabilities to operate as a quantum repeater. This engineering effort includes on-site custom diamond growth (with the Quantum Information and Integrated Nanosystems Group); the development of a scalable silicon-nanophotonics interposer (a chip that merges photonic and electronic functionalities) to control the silicon-vacancy qubit; and integration and packaging of the components into a system that can be cooled to the cryogenic temperatures needed for long-term memory storage. The current system has two memory modules, each capable of holding eight optical qubits.

To test the technologies, the team has been leveraging an optical-fiber test bed leased by the laboratory. This test bed features a 50-kilometer-long telecommunications network fiber currently connecting three nodes: Lincoln Laboratory to MIT campus and MIT campus to Harvard. Local industrial partners can also tap into this fiber as part of the Boston-Area Quantum Network (BARQNET).

"Our goal is to take state-of-the-art research done by our academic partners and transform it into something we can bring outside the lab to test over real channels with real loss," Hamilton says. "All of this infrastructure is critical for doing baseline experiments to get entanglement onto a fiber system and move it between various parties."

Using this test bed, the team, in collaboration with MIT and Harvard researchers, became the first in the world to demonstrate a quantum interaction with a nanophotonic quantum memory across a deployed telecommunications fiber. With the quantum repeater located at Harvard, they sent photons encoded with quantum states from the laboratory, across the fiber, and interfaced them with the silicon-vacancy quantum memory that captured and stored the transmitted quantum states. They measured the electron on the silicon atom to determine how well the quantum states were transferred to the silicon atom's spin-up or spin-down position.

"We looked at our test bed performance for the relevant quantum repeater metrics of distance, efficiency (loss error), fidelity, and scalability and found that we achieved best or near-best for all these metrics, compared to other leading efforts around the world," Dixon says. "Our distance is longer than anybody else has shown; our efficiency is decent, and we think we can further improve it by optimizing some of our test bed components; the read-out qubit from memory matches the qubit we sent with 87.5 percent fidelity; and diamond has an inherent lithographic patterning scalability in which you can imagine putting thousands of qubits onto one small chip." 

The Lincoln Laboratory team is now focusing on combining multiple quantum memories at each node and incorporating additional nodes into the quantum network test bed. Such advances will enable the team to explore quantum networking protocols at a system level. They also look forward to materials science investigations that their Harvard and MIT collaborators are pursuing. These investigations may identify other types of atoms in diamond capable of operating at slightly warmer temperatures for more practical operation.

The nanophotonic quantum memory module was recognized with a 2023 R&D 100 Award.

The popular children's game of telephone is based on a simple premise: The starting player whispers a message into the ear of the next player. That second player then passes along the message to the third person and so on until the message reaches the final recipient, who relays it to the group aloud. Often, what the first person said and the last person heard are laughably different; the information gets garbled along the chain.

Such transmission errors from start to end point are also common in the quantum world. As quantum information bits, or qubits (the analogs of classical bits in traditional digital electronics), make their way over a channel, their quantum states can degrade or be lost entirely. Such decoherence is especially common over longer and longer distances because qubits — whether existing as particles of light (photons), electrons, atoms, or other forms — are inherently fragile, governed by the laws of quantum physics, or the physics of very small objects. At this tiny scale (nanoscale), even slight interactions with their environment can cause qubits to lose their quantum properties and alter the information they store. Like the game of telephone, the original and received messages may not be the same.

"One of the big challenges in quantum networking is how to effectively move these delicate quantum states between multiple quantum systems," says Scott Hamilton, leader of MIT Lincoln Laboratory's Optical and Quantum Communications Technology Group, part of the Communications Systems R&D area. "That's a question we're actively exploring in our group."

As Hamilton explains, today's quantum computing chips contain on the order of 100 qubits. But thousands, if not billions, of qubits are required to make a fully functioning quantum computer, which promises to unlock unprecedented computational power for applications ranging from artificial intelligence and cybersecurity to health care and manufacturing. Interconnecting the chips to make one big computer may provide a viable path forward. On the sensing front, connecting quantum sensors to share quantum information may enable new capabilities and performance gains beyond those of an individual sensor. For example, a shared quantum reference between multiple sensors could be used to more precisely locate radio-frequency emission sources. Space and defense agencies are also interested in interconnecting quantum sensors separated by long ranges for satellite-based position, navigation, and timing systems or atomic clock networks between satellites. For communications, quantum satellites could be used as part of a quantum network architecture connecting local ground-based stations, creating a truly global quantum internet.

However, quantum systems can't be interconnected with existing technology. The communication systems used today to transmit information across a network and connect devices rely on detectors that measure bits and amplifiers that copy bits. These technologies do not work in a quantum network because qubits cannot be measured or copied without destroying the quantum state; qubits exist in a superposition of states between zero and one, as opposed to classical bits, which are in a set state of either zero (off) or one (on). Therefore, researchers have been trying to develop the quantum equivalents of classical amplifiers to overcome transmission and interconnection loss. These equivalents are known as quantum repeaters, and they work similarly in concept to amplifiers, dividing the transmission distance into smaller, more manageable segments to lessen losses.

"Quantum repeaters are a critical technology for quantum networks to successfully send information over lossy links," Hamilton says. "But nobody has made a fully functional quantum repeater yet."

The complexity lies in how quantum repeaters operate. Rather than employing a simple "copy and paste," as classical repeaters do, quantum repeaters work by leveraging a strange quantum phenomenon called entanglement. In quantum entanglement, two particles become strongly connected and correlated across space, no matter the distance between them. If you know the state of one particle in an entangled pair, then you automatically know the state of the other. Entangled qubits can serve as a resource for quantum teleportation, in which quantum information is sent between distant systems without moving actual particles; the information vanishes at one location and reappears at another. Teleportation skips the physical journey along fiber-optic cables and therefore eliminates the associated risk of information loss. Quantum repeaters are what tie everything together: they enable the end-to-end generation of quantum entanglement, and, ultimately, with quantum teleportation, the end-to-end transmission of qubits.

Ben Dixon, a researcher in the Optical and Quantum Communications Technology Group, explains how the process works: "First, you need to generate pairs of specific entangled qubits (called Bell states) and transmit them in different directions across the network link to two separate quantum repeaters, which capture and store these qubits. One of the quantum repeaters then does a two-qubit measurement between the transmitted and stored qubit and an arbitrary qubit that we want to send across the link in order to interconnect the remote quantum systems. The measurement results are communicated to the quantum repeater at the other end of the link; the repeater uses these results to turn the stored Bell state qubit into the arbitrary qubit. Lastly, the repeater can send the arbitrary qubit into the quantum system, thereby linking the two remote quantum systems."

To retain the entangled states, the quantum repeater needs a way to store them — in essence, a memory. In 2020, collaborators at Harvard University demonstrated holding a qubit in a single silicon atom (trapped between two empty spaces left behind by removing two carbon atoms) in diamond. This silicon "vacancy" center in diamond is an attractive quantum memory option. Like other individual electrons, the outermost (valence) electron on the silicon atom can point either up or down, similar to a bar magnet with north and south poles. The direction that the electron points is known as its spin, and the two possible spin states, spin up or spin down, are akin to the ones and zeros used by computers to represent, process, and store information. Moreover, silicon's valence electron can be manipulated with visible light to transfer and store a photonic qubit in the electron spin state. The Harvard researchers did exactly this; they patterned an optical waveguide (a structure that guides light in a desired direction) surrounded by a nanophotonic optical cavity to have a photon strongly interact with the silicon atom and impart its quantum state onto that atom. Collaborators at MIT then showed this basic functionality could work with multiple waveguides; they patterned eight waveguides and successfully generated silicon vacancies inside them all. 

Lincoln Laboratory has since been applying quantum engineering to create a quantum memory module equipped with additional capabilities to operate as a quantum repeater. This engineering effort includes on-site custom diamond growth (with the Quantum Information and Integrated Nanosystems Group); the development of a scalable silicon-nanophotonics interposer (a chip that merges photonic and electronic functionalities) to control the silicon-vacancy qubit; and integration and packaging of the components into a system that can be cooled to the cryogenic temperatures needed for long-term memory storage. The current system has two memory modules, each capable of holding eight optical qubits.

To test the technologies, the team has been leveraging an optical-fiber test bed leased by the laboratory. This test bed features a 50-kilometer-long telecommunications network fiber currently connecting three nodes: Lincoln Laboratory to MIT campus and MIT campus to Harvard. Local industrial partners can also tap into this fiber as part of the Boston-Area Quantum Network (BARQNET).

"Our goal is to take state-of-the-art research done by our academic partners and transform it into something we can bring outside the lab to test over real channels with real loss," Hamilton says. "All of this infrastructure is critical for doing baseline experiments to get entanglement onto a fiber system and move it between various parties."

Using this test bed, the team, in collaboration with MIT and Harvard researchers, became the first in the world to demonstrate a quantum interaction with a nanophotonic quantum memory across a deployed telecommunications fiber. With the quantum repeater located at Harvard, they sent photons encoded with quantum states from the laboratory, across the fiber, and interfaced them with the silicon-vacancy quantum memory that captured and stored the transmitted quantum states. They measured the electron on the silicon atom to determine how well the quantum states were transferred to the silicon atom's spin-up or spin-down position.

"We looked at our test bed performance for the relevant quantum repeater metrics of distance, efficiency (loss error), fidelity, and scalability and found that we achieved best or near-best for all these metrics, compared to other leading efforts around the world," Dixon says. "Our distance is longer than anybody else has shown; our efficiency is decent, and we think we can further improve it by optimizing some of our test bed components; the read-out qubit from memory matches the qubit we sent with 87.5 percent fidelity; and diamond has an inherent lithographic patterning scalability in which you can imagine putting thousands of qubits onto one small chip." 

The Lincoln Laboratory team is now focusing on combining multiple quantum memories at each node and incorporating additional nodes into the quantum network test bed. Such advances will enable the team to explore quantum networking protocols at a system level. They also look forward to materials science investigations that their Harvard and MIT collaborators are pursuing. These investigations may identify other types of atoms in diamond capable of operating at slightly warmer temperatures for more practical operation.

The nanophotonic quantum memory module was recognized with a 2023 R&D 100 Award.

The popular children's game of telephone is based on a simple premise: The starting player whispers a message into the ear of the next player. That second player then passes along the message to the third person and so on until the message reaches the final recipient, who relays it to the group aloud. Often, what the first person said and the last person heard are laughably different; the information gets garbled along the chain.

Such transmission errors from start to end point are also common in the quantum world. As quantum information bits, or qubits (the analogs of classical bits in traditional digital electronics), make their way over a channel, their quantum states can degrade or be lost entirely. Such decoherence is especially common over longer and longer distances because qubits — whether existing as particles of light (photons), electrons, atoms, or other forms — are inherently fragile, governed by the laws of quantum physics, or the physics of very small objects. At this tiny scale (nanoscale), even slight interactions with their environment can cause qubits to lose their quantum properties and alter the information they store. Like the game of telephone, the original and received messages may not be the same.

"One of the big challenges in quantum networking is how to effectively move these delicate quantum states between multiple quantum systems," says Scott Hamilton, leader of MIT Lincoln Laboratory's Optical and Quantum Communications Technology Group, part of the Communications Systems R&D area. "That's a question we're actively exploring in our group."

As Hamilton explains, today's quantum computing chips contain on the order of 100 qubits. But thousands, if not billions, of qubits are required to make a fully functioning quantum computer, which promises to unlock unprecedented computational power for applications ranging from artificial intelligence and cybersecurity to health care and manufacturing. Interconnecting the chips to make one big computer may provide a viable path forward. On the sensing front, connecting quantum sensors to share quantum information may enable new capabilities and performance gains beyond those of an individual sensor. For example, a shared quantum reference between multiple sensors could be used to more precisely locate radio-frequency emission sources. Space and defense agencies are also interested in interconnecting quantum sensors separated by long ranges for satellite-based position, navigation, and timing systems or atomic clock networks between satellites. For communications, quantum satellites could be used as part of a quantum network architecture connecting local ground-based stations, creating a truly global quantum internet.

However, quantum systems can't be interconnected with existing technology. The communication systems used today to transmit information across a network and connect devices rely on detectors that measure bits and amplifiers that copy bits. These technologies do not work in a quantum network because qubits cannot be measured or copied without destroying the quantum state; qubits exist in a superposition of states between zero and one, as opposed to classical bits, which are in a set state of either zero (off) or one (on). Therefore, researchers have been trying to develop the quantum equivalents of classical amplifiers to overcome transmission and interconnection loss. These equivalents are known as quantum repeaters, and they work similarly in concept to amplifiers, dividing the transmission distance into smaller, more manageable segments to lessen losses.

"Quantum repeaters are a critical technology for quantum networks to successfully send information over lossy links," Hamilton says. "But nobody has made a fully functional quantum repeater yet."

The complexity lies in how quantum repeaters operate. Rather than employing a simple "copy and paste," as classical repeaters do, quantum repeaters work by leveraging a strange quantum phenomenon called entanglement. In quantum entanglement, two particles become strongly connected and correlated across space, no matter the distance between them. If you know the state of one particle in an entangled pair, then you automatically know the state of the other. Entangled qubits can serve as a resource for quantum teleportation, in which quantum information is sent between distant systems without moving actual particles; the information vanishes at one location and reappears at another. Teleportation skips the physical journey along fiber-optic cables and therefore eliminates the associated risk of information loss. Quantum repeaters are what tie everything together: they enable the end-to-end generation of quantum entanglement, and, ultimately, with quantum teleportation, the end-to-end transmission of qubits.

Ben Dixon, a researcher in the Optical and Quantum Communications Technology Group, explains how the process works: "First, you need to generate pairs of specific entangled qubits (called Bell states) and transmit them in different directions across the network link to two separate quantum repeaters, which capture and store these qubits. One of the quantum repeaters then does a two-qubit measurement between the transmitted and stored qubit and an arbitrary qubit that we want to send across the link in order to interconnect the remote quantum systems. The measurement results are communicated to the quantum repeater at the other end of the link; the repeater uses these results to turn the stored Bell state qubit into the arbitrary qubit. Lastly, the repeater can send the arbitrary qubit into the quantum system, thereby linking the two remote quantum systems."

To retain the entangled states, the quantum repeater needs a way to store them — in essence, a memory. In 2020, collaborators at Harvard University demonstrated holding a qubit in a single silicon atom (trapped between two empty spaces left behind by removing two carbon atoms) in diamond. This silicon "vacancy" center in diamond is an attractive quantum memory option. Like other individual electrons, the outermost (valence) electron on the silicon atom can point either up or down, similar to a bar magnet with north and south poles. The direction that the electron points is known as its spin, and the two possible spin states, spin up or spin down, are akin to the ones and zeros used by computers to represent, process, and store information. Moreover, silicon's valence electron can be manipulated with visible light to transfer and store a photonic qubit in the electron spin state. The Harvard researchers did exactly this; they patterned an optical waveguide (a structure that guides light in a desired direction) surrounded by a nanophotonic optical cavity to have a photon strongly interact with the silicon atom and impart its quantum state onto that atom. Collaborators at MIT then showed this basic functionality could work with multiple waveguides; they patterned eight waveguides and successfully generated silicon vacancies inside them all. 

Lincoln Laboratory has since been applying quantum engineering to create a quantum memory module equipped with additional capabilities to operate as a quantum repeater. This engineering effort includes on-site custom diamond growth (with the Quantum Information and Integrated Nanosystems Group); the development of a scalable silicon-nanophotonics interposer (a chip that merges photonic and electronic functionalities) to control the silicon-vacancy qubit; and integration and packaging of the components into a system that can be cooled to the cryogenic temperatures needed for long-term memory storage. The current system has two memory modules, each capable of holding eight optical qubits.

To test the technologies, the team has been leveraging an optical-fiber test bed leased by the laboratory. This test bed features a 50-kilometer-long telecommunications network fiber currently connecting three nodes: Lincoln Laboratory to MIT campus and MIT campus to Harvard. Local industrial partners can also tap into this fiber as part of the Boston-Area Quantum Network (BARQNET).

"Our goal is to take state-of-the-art research done by our academic partners and transform it into something we can bring outside the lab to test over real channels with real loss," Hamilton says. "All of this infrastructure is critical for doing baseline experiments to get entanglement onto a fiber system and move it between various parties."

Using this test bed, the team, in collaboration with MIT and Harvard researchers, became the first in the world to demonstrate a quantum interaction with a nanophotonic quantum memory across a deployed telecommunications fiber. With the quantum repeater located at Harvard, they sent photons encoded with quantum states from the laboratory, across the fiber, and interfaced them with the silicon-vacancy quantum memory that captured and stored the transmitted quantum states. They measured the electron on the silicon atom to determine how well the quantum states were transferred to the silicon atom's spin-up or spin-down position.

"We looked at our test bed performance for the relevant quantum repeater metrics of distance, efficiency (loss error), fidelity, and scalability and found that we achieved best or near-best for all these metrics, compared to other leading efforts around the world," Dixon says. "Our distance is longer than anybody else has shown; our efficiency is decent, and we think we can further improve it by optimizing some of our test bed components; the read-out qubit from memory matches the qubit we sent with 87.5 percent fidelity; and diamond has an inherent lithographic patterning scalability in which you can imagine putting thousands of qubits onto one small chip." 

The Lincoln Laboratory team is now focusing on combining multiple quantum memories at each node and incorporating additional nodes into the quantum network test bed. Such advances will enable the team to explore quantum networking protocols at a system level. They also look forward to materials science investigations that their Harvard and MIT collaborators are pursuing. These investigations may identify other types of atoms in diamond capable of operating at slightly warmer temperatures for more practical operation.

The nanophotonic quantum memory module was recognized with a 2023 R&D 100 Award.

The popular children's game of telephone is based on a simple premise: The starting player whispers a message into the ear of the next player. That second player then passes along the message to the third person and so on until the message reaches the final recipient, who relays it to the group aloud. Often, what the first person said and the last person heard are laughably different; the information gets garbled along the chain.

Such transmission errors from start to end point are also common in the quantum world. As quantum information bits, or qubits (the analogs of classical bits in traditional digital electronics), make their way over a channel, their quantum states can degrade or be lost entirely. Such decoherence is especially common over longer and longer distances because qubits — whether existing as particles of light (photons), electrons, atoms, or other forms — are inherently fragile, governed by the laws of quantum physics, or the physics of very small objects. At this tiny scale (nanoscale), even slight interactions with their environment can cause qubits to lose their quantum properties and alter the information they store. Like the game of telephone, the original and received messages may not be the same.

"One of the big challenges in quantum networking is how to effectively move these delicate quantum states between multiple quantum systems," says Scott Hamilton, leader of MIT Lincoln Laboratory's Optical and Quantum Communications Technology Group, part of the Communications Systems R&D area. "That's a question we're actively exploring in our group."

As Hamilton explains, today's quantum computing chips contain on the order of 100 qubits. But thousands, if not billions, of qubits are required to make a fully functioning quantum computer, which promises to unlock unprecedented computational power for applications ranging from artificial intelligence and cybersecurity to health care and manufacturing. Interconnecting the chips to make one big computer may provide a viable path forward. On the sensing front, connecting quantum sensors to share quantum information may enable new capabilities and performance gains beyond those of an individual sensor. For example, a shared quantum reference between multiple sensors could be used to more precisely locate radio-frequency emission sources. Space and defense agencies are also interested in interconnecting quantum sensors separated by long ranges for satellite-based position, navigation, and timing systems or atomic clock networks between satellites. For communications, quantum satellites could be used as part of a quantum network architecture connecting local ground-based stations, creating a truly global quantum internet.

However, quantum systems can't be interconnected with existing technology. The communication systems used today to transmit information across a network and connect devices rely on detectors that measure bits and amplifiers that copy bits. These technologies do not work in a quantum network because qubits cannot be measured or copied without destroying the quantum state; qubits exist in a superposition of states between zero and one, as opposed to classical bits, which are in a set state of either zero (off) or one (on). Therefore, researchers have been trying to develop the quantum equivalents of classical amplifiers to overcome transmission and interconnection loss. These equivalents are known as quantum repeaters, and they work similarly in concept to amplifiers, dividing the transmission distance into smaller, more manageable segments to lessen losses.

"Quantum repeaters are a critical technology for quantum networks to successfully send information over lossy links," Hamilton says. "But nobody has made a fully functional quantum repeater yet."

The complexity lies in how quantum repeaters operate. Rather than employing a simple "copy and paste," as classical repeaters do, quantum repeaters work by leveraging a strange quantum phenomenon called entanglement. In quantum entanglement, two particles become strongly connected and correlated across space, no matter the distance between them. If you know the state of one particle in an entangled pair, then you automatically know the state of the other. Entangled qubits can serve as a resource for quantum teleportation, in which quantum information is sent between distant systems without moving actual particles; the information vanishes at one location and reappears at another. Teleportation skips the physical journey along fiber-optic cables and therefore eliminates the associated risk of information loss. Quantum repeaters are what tie everything together: they enable the end-to-end generation of quantum entanglement, and, ultimately, with quantum teleportation, the end-to-end transmission of qubits.

Ben Dixon, a researcher in the Optical and Quantum Communications Technology Group, explains how the process works: "First, you need to generate pairs of specific entangled qubits (called Bell states) and transmit them in different directions across the network link to two separate quantum repeaters, which capture and store these qubits. One of the quantum repeaters then does a two-qubit measurement between the transmitted and stored qubit and an arbitrary qubit that we want to send across the link in order to interconnect the remote quantum systems. The measurement results are communicated to the quantum repeater at the other end of the link; the repeater uses these results to turn the stored Bell state qubit into the arbitrary qubit. Lastly, the repeater can send the arbitrary qubit into the quantum system, thereby linking the two remote quantum systems."

To retain the entangled states, the quantum repeater needs a way to store them — in essence, a memory. In 2020, collaborators at Harvard University demonstrated holding a qubit in a single silicon atom (trapped between two empty spaces left behind by removing two carbon atoms) in diamond. This silicon "vacancy" center in diamond is an attractive quantum memory option. Like other individual electrons, the outermost (valence) electron on the silicon atom can point either up or down, similar to a bar magnet with north and south poles. The direction that the electron points is known as its spin, and the two possible spin states, spin up or spin down, are akin to the ones and zeros used by computers to represent, process, and store information. Moreover, silicon's valence electron can be manipulated with visible light to transfer and store a photonic qubit in the electron spin state. The Harvard researchers did exactly this; they patterned an optical waveguide (a structure that guides light in a desired direction) surrounded by a nanophotonic optical cavity to have a photon strongly interact with the silicon atom and impart its quantum state onto that atom. Collaborators at MIT then showed this basic functionality could work with multiple waveguides; they patterned eight waveguides and successfully generated silicon vacancies inside them all. 

Lincoln Laboratory has since been applying quantum engineering to create a quantum memory module equipped with additional capabilities to operate as a quantum repeater. This engineering effort includes on-site custom diamond growth (with the Quantum Information and Integrated Nanosystems Group); the development of a scalable silicon-nanophotonics interposer (a chip that merges photonic and electronic functionalities) to control the silicon-vacancy qubit; and integration and packaging of the components into a system that can be cooled to the cryogenic temperatures needed for long-term memory storage. The current system has two memory modules, each capable of holding eight optical qubits.

To test the technologies, the team has been leveraging an optical-fiber test bed leased by the laboratory. This test bed features a 50-kilometer-long telecommunications network fiber currently connecting three nodes: Lincoln Laboratory to MIT campus and MIT campus to Harvard. Local industrial partners can also tap into this fiber as part of the Boston-Area Quantum Network (BARQNET).

"Our goal is to take state-of-the-art research done by our academic partners and transform it into something we can bring outside the lab to test over real channels with real loss," Hamilton says. "All of this infrastructure is critical for doing baseline experiments to get entanglement onto a fiber system and move it between various parties."

Using this test bed, the team, in collaboration with MIT and Harvard researchers, became the first in the world to demonstrate a quantum interaction with a nanophotonic quantum memory across a deployed telecommunications fiber. With the quantum repeater located at Harvard, they sent photons encoded with quantum states from the laboratory, across the fiber, and interfaced them with the silicon-vacancy quantum memory that captured and stored the transmitted quantum states. They measured the electron on the silicon atom to determine how well the quantum states were transferred to the silicon atom's spin-up or spin-down position.

"We looked at our test bed performance for the relevant quantum repeater metrics of distance, efficiency (loss error), fidelity, and scalability and found that we achieved best or near-best for all these metrics, compared to other leading efforts around the world," Dixon says. "Our distance is longer than anybody else has shown; our efficiency is decent, and we think we can further improve it by optimizing some of our test bed components; the read-out qubit from memory matches the qubit we sent with 87.5 percent fidelity; and diamond has an inherent lithographic patterning scalability in which you can imagine putting thousands of qubits onto one small chip." 

The Lincoln Laboratory team is now focusing on combining multiple quantum memories at each node and incorporating additional nodes into the quantum network test bed. Such advances will enable the team to explore quantum networking protocols at a system level. They also look forward to materials science investigations that their Harvard and MIT collaborators are pursuing. These investigations may identify other types of atoms in diamond capable of operating at slightly warmer temperatures for more practical operation.

The nanophotonic quantum memory module was recognized with a 2023 R&D 100 Award.

MIT scientists and their colleagues have created a simple superconducting device that could transfer current through electronic devices much more efficiently than is possible today. As a result, the new diode, a kind of switch, could dramatically cut the amount of energy used in high-power computing systems, a major problem that is estimated to become much worse. Even though it is in the early stages of development, the diode is more than twice as efficient as similar ones reported by others. It could even be integral to emerging quantum computing technologies.

The work, which is reported in the July 13 online issue of Physical Review Letters, is also the subject of a news story in Physics Magazine.

“This paper showcases that the superconducting diode is an entirely solved problem from an engineering perspective,” says Philip Moll, director of the Max Planck Institute for the Structure and Dynamics of Matter in Germany. Moll was not involved in the work. “The beauty of [this] work is that [Moodera and colleagues] obtained record efficiencies without even trying [and] their structures are far from optimized yet.”

“Our engineering of a superconducting diode effect that is robust and can operate over a wide temperature range in simple systems can potentially open the door for novel technologies,” says Jagadeesh Moodera, leader of the current work and a senior research scientist in MIT’s Department of Physics. Moodera is also affiliated with the Materials Research Laboratory, the Francis Bitter Magnet Laboratory, and the Plasma Science and Fusion Center (PSFC).

The nanoscopic rectangular diode — about 1,000 times thinner than the diameter of a human hair — is easily scalable. Millions could be produced on a single silicon wafer.

Toward a superconducting switch

Diodes, devices that allow current to travel easily in one direction but not in the reverse, are ubiquitous in computing systems. Modern semiconductor computer chips contain billions of diode-like devices known as transistors. However, these devices can get very hot due to electrical resistance, requiring vast amounts of energy to cool the high-power systems in the data centers behind myriad modern technologies, including cloud computing. According to a 2018 news feature in Nature, these systems could use nearly 20 percent of the world’s power in 10 years.

As a result, work toward creating diodes made of superconductors has been a hot topic in condensed matter physics. That’s because superconductors transmit current with no resistance at all below a certain low temperature (the critical temperature), and are therefore much more efficient than their semiconducting cousins, which have noticeable energy loss in the form of heat.

Until now, however, other approaches to the problem have involved much more complicated physics. “The effect we found is due [in part] to a ubiquitous property of superconductors that can be realized in a very simple, straightforward manner. It just stares you in the face,” says Moodera.

Says Moll of the Max Planck Institute, “The work is an important counterpoint to the current fashion to associate superconducting diodes [with] exotic physics, such as finite-momentum pairing states. While in reality, a superconducting diode is a common and widespread phenomenon present in classical materials, as a result of certain broken symmetries.”

A somewhat serendipitous discovery

In 2020 Moodera and colleagues observed evidence of an exotic particle pair known as Majorana fermions. These particle pairs could lead to a new family of topological qubits, the building blocks of quantum computers. While pondering approaches to creating superconducting diodes, the team realized that the material platform they developed for the Majorana work might also be applied to the diode problem.

They were right. Using that general platform, they developed different iterations of superconducting diodes, each more efficient than the last. The first, for example, consisted of a nanoscopically thin layer of vanadium, a superconductor, which was patterned into a structure common to electronics (the Hall bar). When they applied a tiny magnetic field comparable to the Earth’s magnetic field, they saw the diode effect — a giant polarity dependence for current flow.

They then created another diode, this time layering a superconductor with a ferromagnet (a ferromagnetic insulator in their case), a material that produces its own tiny magnetic field. After applying a tiny magnetic field to magnetize the ferromagnet so that it produces its own field, they found an even bigger diode effect that was stable even after the original magnetic field was turned off.

Ubiquitous properties

The team went on to figure out what was happening.

In addition to transmitting current with no resistance, superconductors also have other, less well-known but just as ubiquitous properties. For example, they don’t like magnetic fields getting inside. When exposed to a tiny magnetic field, superconductors produce an internal supercurrent that induces its own magnetic flux that cancels the external field, thereby maintaining their superconducting state. This phenomenon, known as the Meissner screening effect, can be thought of as akin to our bodies’ immune system releasing antibodies to fight the infection of bacteria and other pathogens. This works, however, only up to some limit. Similarly, superconductors cannot entirely keep out large magnetic fields.

The diodes the team created make use of this universal Meissner screening effect. The tiny magnetic field they applied — either directly, or through the adjacent ferromagnetic layer — activates the material’s screening current mechanism for expelling the external magnetic field and maintaining superconductivity.

The team also found that another key factor in optimizing these superconductor diodes is tiny differences between the two sides, or edges, of the diode devices. These differences “create some sort of asymmetry in the way the magnetic field enters the superconductor,” Moodera says.

By engineering their own form of edges on diodes to optimize these differences — for example, one edge with sawtooth features, while the other edge not intentionally altered — the team found that they could increase the efficiency from 20 percent to more than 50 percent. This discovery opens the door for devices whose edges could be “tuned” for even higher efficiencies, Moodera says.

In sum, the team discovered that the edge asymmetries within superconducting diodes, the ubiquitous Meissner screening effect found in all superconductors, and a third property of superconductors known as vortex pinning all came together to produce the diode effect.

“It is fascinating to see how inconspicuous yet ubiquitous factors can create a significant effect in observing the diode effect,” says Yasen Hou, first author of the paper and a postdoc at the Francis Bitter Magnet Laboratory and the PSFC. “What’s more exciting is that [this work] provides a straightforward approach with huge potential to further improve the efficiency.”

Christoph Strunk is a professor at the University of Regensburg in Germany. Says Strunk, who was not involved in the research, “the present work demonstrates that the supercurrent in simple superconducting strips can become nonreciprocal. Moreover, when combined with a ferromagnetic insulator, the diode effect can even be maintained in the absence of an external magnetic field. The rectification direction can be programmed by the remnant magnetization of the magnetic layer, which may have high potential for future applications. The work is important and appealing both from the basic research and from the applications point of view.”

Teenage contributors

Moodera noted that the two researchers who created the engineered edges did so while still in high school during a summer at Moodera’s lab. They are Ourania Glezakou-Elbert of Richland, Washington, who will be going to Princeton University this fall, and Amith Varambally of Vestavia Hills, Alabama, who will be entering Caltech.

Says Varambally, “I didn't know what to expect when I set foot in Boston last summer, and certainly never expected to [be] a coauthor in a Physical Review Letters paper.

“Every day was exciting, whether I was reading dozens of papers to better understand the diode phenomena, or operating machinery to fabricate new diodes for study, or engaging in conversations with Ourania, Dr. Hou, and Dr. Moodera about our research.

“I am profoundly grateful to Dr. Moodera and Dr. Hou for providing me with the opportunity to work on such a fascinating project, and to Ourania for being a great research partner and friend.”

In addition to Moodera and Hou, corresponding authors of the paper are professors Patrick A. Lee of the MIT Department of Physics and Akashdeep Kamra of Autonomous University of Madrid. Other authors from MIT are Liang Fu and Margarita Davydova of the Department of Physics, and Hang Chi, Alessandro Lodesani, and Yingying Wu, all of the Francis Bitter Magnet Laboratory and the Plasma Science and Fusion Center. Chi is also affiliated with the U.S. Army CCDC Research Laboratory.

Authors also include Fabrizio Nichele, Markus F. Ritter, and Daniel Z. Haxwell of IBM Research Europe; Stefan Ilić of Materials Physics Center (CFM-MPC); and F. Sebastian Bergeret of CFM-MPC and Donostia International Physics Center.

This work was supported by the Air Force Office of Sponsored Research, the Office of Naval Research, the National Science Foundation, and the Army Research Office. Additional funders are the European Research Council, the European Union’s Horizon 2020 Research and Innovation Framework Programme, the Spanish Ministry of Science and Innovation, the A. v. Humboldt Foundation, and the Department of Energy’s Office of Basic Sciences.