&shell; Physics 16, 103
Device-selective coupling with left- and right-hand propagation techniques may pave the way for quantum computing based on high-level circuits.
If a source emits a wave that scatters an object and is measured by a detector, the principle of redundancy states that the measured signal will not be changed if the source and detector change position. Symmetry is a common feature in all physical systems, but in some cases it is a contradiction. For example, to create an isolator – a device that allows signals to pass through one side but not the other – the connection must be broken. Unequal instruments like this, which are clearly defined or “smart” in their emission or absorption – are valuable in many ways. Recently, nonlinear materials have been used in superconducting electronic systems used in quantum computing, but all have had problems. Now Chaitali Joshi and his colleagues at the California Institute of Technology have created a simple irreversible device: an “artificial atom” made from a superconducting region, which can be combined only with left or right signals in a microwave waveguide. [1]. This chiral structure can be used in quantum networks to control the flow of information between multiple artificial atoms coupled to waveguides.
Superconducting circuits are one of the most popular platforms for quantum computing [2]. But they can benefit from having a constant flow of things that will help them stay cool and aware of the volume [2–5]. Previous work has demonstrated flexible devices that control the propagation of visible light using organic atoms and other single-photon emitters. [3]. In that work, light is confined to a planar waveguide that limits the spread of light to certain areas. An atom or other emitter coupled to a waveguide can be made to only emit and absorb light traveling in one direction.
However, this optical setup does not work for superconducting circuits and the low-frequency microwaves that are associated with them. [6]. Because natural atoms are not very flexible in microwave emitters, researchers often use artificial atoms made from large particles arranged in a circular pattern. Like real atoms, these well-conducting circuits have ground states and excited states, which can be set up for use. The problem, however, is that the coupling between artificial atoms and microwave waveguides does not provide the same dependence that is observed. [6]. Researchers have developed other methods, but the existing chiral structures of superconducting circuits are often more complex, complex, or limited in other ways. [2].
Some of the more recently developed and demonstrated therapeutic strategies use “supermolecules,” which are artificial atoms joined together. [7, 8]. Each atom is connected to a waveguide at a different location. Interference changes the emission and absorption of each atom, thus causing propagation through the waveguide to be suppressed or amplified. Joshi and his colleagues have taken this idea and simplified it so that only one artificial atom is needed as the emitter. He created an artificial atom that couples into a 1D waveguide at several points separated by a distance of one meter – realizing the expansion of the concept of a giant molecule in the form of a “giant atom” [9, 10].
In order to achieve the interference required by using a single emitter, the researchers not only needed to establish the distance between the points of connection, but also to establish the field of connection at each point. They achieved this by using superconducting superconducting atoms as couplers between the emitter atom and the waveguide. Using a magnetic field, the band can manipulate the coupler atoms in a way that controls the coupling between the emitter and the waveguide. The relative phase between the modulations of the two couplers produced an important phase difference that either allows forward- or backward-propagation of light through the waveguide (fig. 1). The phase difference in the transition was easy to dial, so the interaction variable could be easily switched from one side to the other.
The researchers demonstrated the properties of their device in several experiments. First, they measured the propagation of a weak photonic signal at resonance with an atom. This measurement showed that forward or backward photon coupling is reduced from high to low when the relative phase of the transition signals is varied. Next, the researchers increased the signal strength of the probe to achieve the first transition of the atom. At that time, he observed the so-called Mollow triplet, a well-known quantum-optical phenomenon, thus showing that the chirality of interactions was not limited to the operation of a single photon. Finally, they investigated the transition between the first and second excited state of an artificial atom, showing that the interaction between these states can also be made chiral. They also observed how the field of probe photons changed depending on the position of the atom. In doing so, he discovered a clear gate between the atom and the photon.
A natural result would be to show that the new chiral device can transmit more than just the simple movement of microwave photons. For example, the team could try to transfer a quantum state from one artificial atom to another and back. Such a demonstration would be an important step in the construction of a quantum network with artificial superconducting atoms. Setting up a large network will also need to suppress lossy channels during setup and increase the coupling strength between artificial atoms and waveguides. This improvement should, however, be easy to identify.
References
- C. Joshi and al.“Resonance fluorescence of a chiral atomic structure,” Phys. Rev. X 13021039 (2023).
- X. Gu and al.“Microwave films with superconducting quantum circuits,” Phys. Rep. 718-7191 (2017).
- P. Lodahl and al.“Chiral quantum optics,” Nature 541473 (2017).
- JI Cirac and al.“Quantum transmission and transmission between remote nodes in a quantum network,” Phys. Rev. Lett. 783221 (1997).
- HJ Kimble, “The quantum Internet,” Nature 4531023 (2008).
- M. Casariego and al.“Quantum microwave propagation: toward applications in communication and hearing,” Quantum Sci. Technol. 8023001 (2023).
- P.O. Guimond and al.“Unidirectional on-chip photonic imaging of superconducting circuits,” Company opinion NPJ Quantum Inf. 632 (2020).
- B. I agree and al.“Toward control of microwave photon emission using waveguide quantum electrodynamics,” Nat. Phys. 19394 (2023).
- AF Kockum, “Quantum models with large atoms – the first five years,” International Symposium on Mathematics, Quantum Theory, and Cryptography 125 (2020).
- B. I agree and al.“Waveguide quantum electrodynamics with large superconducting atoms,” Nature 583775 (2020).
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