Phenomena of the quantum world, which often seem bizarre, have long been used in technology. For example,
What is the problem?
However, to use a quantum computer to its full potential, all entangled particles must work together. We are talking about the basic elements for calculations - qubits.
Photons—particles—are ideal for this.Sveta. The point is that they are quite “strong” by nature and are easy to manipulate. Now, researchers at the Max Planck Institute of Quantum Optics (MPQ) in Garching are closer to making photons suitable for practical work, such as quantum computing. Scientists have generated 14 entangled photons in a specific way with high efficiency.
How was the experiment?
The peculiarity of the new experiment is thatScientists used a single atom to emit photons and "intertwine" them in a specific way. To do this, researchers at the Max Planck Institute placed a rubidium atom in the center of an optical resonator—a kind of “echo chamber” for electromagnetic waves.
Experimental setup with a vacuum chamber on an optical table. Photo: MPQ
With the help of laser radiation of a certainfrequencies they accurately determined the state of the atom. Using the extra momentum, the scientists also deliberately caused the emission of a photon, which is associated with the quantum state of the atom.
During the experiment, scientists repeated thisprocess several times. In the intervals, the atom was manipulated in a certain way—in other words, “rotated.” In this way, physicists created a chain of 14 particles of light, which became entangled with each other due to the rotation of atoms and were brought into the desired state.
At the moment, 14 interconnected particles of light is the largest number of entangled photons that have so far been generated in the laboratory.
Two possibilities of the new method
But not only the number of entangled photons is very important for the development of powerful quantum computers - the way they are generated is also very different from conventional methods.
"Since the chain of photons arosefrom a single atom, it could be produced in a deterministic manner,” the scientists explain in a press release for the new study. This means that, in principle, each pulse actually delivers a photon “in place” with the desired properties.
Until now, the entanglement of these particles is usuallyoccurred in special nonlinear crystals. The problem is that there light particles are generated randomly and cannot be controlled. As a result, this limits the number of particles that can be combined in a collective interaction.
Installation of an optical resonator in vacuum. A single rubidium atom is trapped between conical mirrors inside the holder. Photo: MPQ
On the other hand, the method developed innew research, makes it possible to generate virtually any number of entangled photons. Moreover, it is very effective. This means that it can be applied in practice in the future. Thus, scientists measured the resulting chain of photons and proved its 50 percent efficiency.
Almost every second "button press" on an atomrubidium delivered a usable light particle. In previous experiments, scientists could not achieve this. The new work removes a long-standing obstacle to scalable measurement-based quantum computing, the scientists emphasize.
What's next?
Now MPQ employees want to solve another problemthe problem of the quantum future. For example, complex computational operations will require at least two atoms as photon sources in the cavity. “We are already working on solving this problem,” the scientists explained in a statement.
Max Planck's collaborators also stated thatThe technology can be used not only for quantum computing. For example, it will be useful in quantum communications—transmitting information over optical fiber with protection from eavesdropping. Due to optical effects such as scattering and absorption, light in optical fiber is “lost” during propagation. This greatly limits the distance over which data can be transmitted.
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