When two atoms are placed in a small cavity surrounded by a mirror, they can absorb a single photon at the same time. Researchers at an international collaborative research group have found that the opposite of this process is also possible: two atoms excite one photon. According to the research team, this process can be used to transmit information in quantum circuits or computers.
Physicists have long known that an atom can absorb or emit two photons simultaneously. These two-photon, one-atom processes are widely used in spectroscopy and for making entangled photons for use in quantum devices. However, Salvatore Savasta, a partner at the University of Messina in Italy, suspects that two atoms can absorb one photon. When Savasta asked his PhD student, Luigi Garziano conducted the simulation. Garziano's simulation shows that this is possible and Savasta was very excited when he heard the news.
A single pair of two?
Their simulation found that this phenomenon took place when the resonance frequency of an optical cavity containing atoms was twice the transition frequency of a single atom. For example, in a cavity, the resonant frequency is three times the atomic transition, three atoms can simultaneously absorb or emit a photon. The size of the cavity is made up of this resonant frequency, which must be a standing wave. According to the researchers' calculations, two atoms oscillate back and forth between the ground state and the excited state. In fact, the atoms will first co-absorb photons, ending in their excited state, co-emitting a single photon back to their ground state. The loop will be repeated. In addition, they found that combined absorption and emission can occur on more than two atoms.
Quantum switch
A two-atom, one-photon system can act as a switch to send information in quantum circuits, Savasta said. One atom acts as a superposition of the ground and excited states of the quantum bit encoding information. Passing information outside the cavity, the qubit needs information that is passed in the cavity to the photon. The second atom can be used to control whether to send information bits. If the transition frequency of the second atom is tuned to half the resonant frequency of the cavity, both atoms can jointly absorb and emit a single photon, which will contain the encoded information to be transmitted. To ensure that atoms do not reabsorb photons, the resonant frequency of the atoms can be changed by applying an external magnetic field.
Savasta's group has started looking for collaborators based on theoretical predictions from lab experiments that look for experiments that can actually experiment with atoms. Savasta plans to use artificial atoms: that is, to have a quantum energy level and a similar atomic state Characteristics of superconducting particles, but its transition energy can be more easily adjusted by the experimenter. In addition, the control of real atoms involves expensive techniques, while man-made atoms can be inexpensively fabricated on solid-state chips. "The real atom is only good proof of the principle experiment," he said.
Savasta predicts that their collaborators will be able to experiment successfully within a year. "We think this experiment is better within the current art, especially if superconducting qubits are used," he said.
Tatjana Wilk, Max Planck's Gachen Institute for Quantum Optics, cautioned that she was not involved in the study, saying that the excited states of atoms may not last long enough for actual quantum devices.
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