April 17, 2018

Purdue contributes to experiments on light-matter interactions for potential quantum technology applications

WEST LAFAYETTE, Ind. — Purdue researchers collaborated in a Rice University-led study detecting a quantum shift that results from the strong coupling of light and an ultra-high mobility two-dimensional electron gas rotating in opposite directions.

The work, published on April 16 in Nature Photonics, describes a system predicted to go into a new ground state (or state of lowest energy) that physicists could use to study phase transitions and possibly harness for the development of quantum bits for advanced computing. Researchers found that inducing strong coupling of light and matter in the form of a two-dimensional electron gas leads to a quantum interaction of counter-rotating fields called the Bloch-Siegert shift.

 “Our collaborators at Rice have developed a method to probe a light-matter system in a way not previously realized,” said Michael Manfra, professor of physics and astronomy who led Purdue’s team.  “The combined material, experimental and theoretical advances really pave the way for many new discoveries.”

In order to detect and measure the shift, Rice researchers placed the electron gas in a cavity and coupled it to circularly polarized light. Purdue visiting scholar Geoff Gardner and graduate student Saeed Fallahi fabricated the electron gas in which the Bloch-Siegert shift was observed. The electrons then hybridized with a resonant electromagnetic field to form so-called Landau polaritons.

 “It is great fun to participate in a joint effort that combines Rice’s expertise in light-matter coupling with Purdue’s capabilities in materials physics”, said Manfra, whose Station Q Purdue group focuses on several aspects of quantum computing in solid-state systems. 

Landau polaritons, studied by Junichiro Kono’s group at Rice, constitute a two-level system driven by a resonant electromagnetic field.  Such systems potentially find applications in quantum technologies relevant to quantum computing.

Writer: Kayla Wiles, 765-494-2432, wiles5@purdue.edu

Sources: Michael Manfra, 765-494-3016, mmanfra@purdue.edu

Geoff Gardner, geoff@purdue.edu

Note to journalists: For a full-text copy of the paper, please contact Kayla Wiles, Purdue News Service, at wiles5@purdue.edu.


Vacuum Bloch-Siegert shift in Landau polaritons with ultra-high cooperativity

Xinwei Li1, Motoaki Bamba2, Qi Zhang 3, Saeed Fallahi4, Geoff C. Gardner4, Weilu Gao 1,

Minhan Lou1, Katsumasa Yoshioka5, Michael J. Manfra4 and Junichiro Kono 1

1Rice University, Houston, TX, USA

2Osaka University, Osaka, Japan

3Argonne National Laboratories, Lemont, IL, USA

4Purdue University, West Lafayette, IN, USA

5Yokohama National Univerity, Yokohama, Japan

doi: 10.1038/s41566-018-0153-0

A two-level system resonantly interacting with an a.c. magnetic or electric field constitutes the physical basis of diverse phenomena and technologies. However, Schrödinger’s equation for this seemingly simple system can be solved exactly only under the rotating-wave approximation, which neglects the counter-rotating field component. When the a.c. field is sufficiently strong, this approximation fails, leading to a resonance-frequency shift known as the Bloch–Siegert shift. Here, we report the vacuum Bloch–Siegert shift, which is induced by the ultra-strong coupling of matter with the counter-rotating component of the vacuum fluctuation field in a cavity. Specifically, an ultra-high-mobility two-dimensional electron gas inside a high-Q terahertz cavity in a quantizing magnetic field revealed ultra-narrow Landau polaritons, which exhibited a vacuum Bloch–Siegert shift up to 40 GHz. This shift, clearly distinguishable from the photon-field self-interaction effect, represents a unique manifestation of a strong-field phenomenon without a strong field.

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