First Ultrafast, Room‑Temperature All‑Optical Transistor Sets New Benchmark

Modern digital computers have reshaped society, yet the core technologies that power them still have significant room for evolution. As data volumes swell and artificial‑intelligence workloads grow, the demand for more powerful, efficient computing platforms intensifies.

The electronic transistor and the von Neumann architecture remain the twin pillars of today’s silicon‑based systems. By packing ever more transistors onto smaller chips, we have built devices—smartphones, laptops, and servers—that deliver orders‑of‑magnitude more computational power than the early computers that landed humans on the Moon. Still, these technologies are not the final chapter in computing’s story.

In recent years a renaissance of interest in radically different components and architectures has emerged, encompassing AI‑optimized hardware, in‑memory and analog computing, and quantum processors. IBM Research has long been at the forefront of exploring such breakthrough concepts, probing the physical limits that could shape tomorrow’s information‑processing infrastructure.

Now, the IBM Research team in Zurich, in collaboration with researchers at the Skolkovo Institute of Science and Technology (SIST) and the University of Southampton, has announced the first cascadable, all‑optical transistor that operates at ambient temperature. This milestone was achieved by harnessing the unique properties of an organic semiconducting polymer—methyl‑substituted ladder‑type poly‑[paraphenylene] (MeLPPP)—to create a microcavity that allows one laser beam to switch, amplify, or suppress another.

The breakthrough is featured on the cover of the latest issue of the peer‑reviewed journal Nature Photonics.

Why It Matters

All‑optical components that process information exclusively with light promise dramatically faster switching, lower power consumption, and new functionalities such as routing “flying qubits” for quantum communication or enabling blind quantum computing. Building such devices, however, has proven notoriously difficult, and the quest for an all‑optical computer has spanned roughly five decades.

To switch or amplify an optical signal with another optical signal, a mediating material is required, because photons in a vacuum do not interact. In this transistor, the interaction is facilitated by quasi‑particles called exciton‑polariton, which arise in the organic semiconductor. A 35‑nanometer layer of MeLPPP is sandwiched between two highly reflective mirrors to form an optical cavity where exciton‑polaritons are generated using a laser. An exciton‑polariton is a hybrid of an electron‑hole pair (exciton) and a photon, placing this device squarely in the emerging field of organic polariton transistors.

This transistor is the first of its kind to operate at room temperature, delivering an unprecedented 6,500‑fold optical signal amplification from a device only a few micrometers long. That amplification is 330 times greater than what has been achieved in inorganic counterparts, enabling the necessary cascadability for logic operations. Experiments also revealed the highest net optical gain ever recorded for an optical transistor—approximately 10 dB / µm.

Furthermore, the device switches in the sub‑picosecond regime, achieving speeds in the multi‑terahertz range without the need for cryogenic cooling—a major advantage over earlier all‑optical systems.

Crucially, the organic polariton transistor eliminates a practical limitation that hampers inorganic designs: the pump laser in inorganic microcavities must be incident at a precise angle to trigger the transistor. In the organic device, the pump laser can be directed from virtually any angle, offering unprecedented flexibility for integrating the transistor into fiber‑pigtailed systems or planar on‑chip circuits.

How We Did It

The energy landscape of exciton‑polariton states is defined by several polariton branches that arise from strong light‑matter coupling between cavity photons and excitons. Our strategy leveraged the bosonic nature of exciton‑polariton and the presence of pronounced vibrational modes in the organic semiconductor to induce an avalanche‑like relaxation of hot excitons into the lowest polariton branch (the ground state). This vibron‑mediated relaxation pathway was designed to dominate over competing internal conversion channels, and the experiments confirmed its effectiveness.

Achieving Truly Giant Amplification

In the first step, we used a non‑resonant pump laser to generate a high density of hot excitons. The pump wavelength was tuned to produce excitons whose energy lay exactly one vibronic quantum above the lower polariton branch. The chosen vibronic mode corresponds to a “breathing” motion of the aromatic rings in the polymer. Because the strongly localized excitons exhibit a broad momentum distribution, the pump’s in‑plane momentum component is largely irrelevant; thus, the pump can be applied at essentially any angle, avoiding the stringent phase‑matching constraints of inorganic microcavities.

As the pump excitation density increased, we observed a clear transition from the linear to the nonlinear regime, with a threshold of approximately 82 µJ cm⁻². By seeding the ground polariton state with a weak control beam (≈ 20 nJ cm⁻²—over three orders of magnitude weaker than the non‑resonant pump), we lowered the condensation threshold nearly twofold and increased the exciton‑to‑polariton relaxation rate by a factor of 50 under the same pump conditions.

Ultrafast All‑Optical Switching

Sub‑picosecond switching times result from the combination of ultrafast exciton relaxation inherent to organic semiconductors and the sub‑picosecond cavity lifetime. In our setup, the pump beam establishes the address state, gated by the control beam. With a control energy of only 1 pJ, we achieved a maximum extinction ratio of 17 dB (ratio of the ‘1’ to ‘0’ intensity levels) and a switching response time of roughly 500 fs.

Finally, we demonstrated the transistor’s cascadability by implementing a two‑stage amplification scheme. The emission from the first stage’s condensate was redirected onto the chip and further amplified by a second pump. Using cascaded amplification, we also realized OR and AND logic gates by coupling three polariton transistors on the same chip within a single pump‑double‑probe configuration.

Summary

These experiments showcase vibron‑mediated dynamic polariton condensation in an organic microcavity at ambient conditions, enabling all‑optical amplification, sub‑picosecond switching, and cascadable logic operations. The combination of reliable, ultrafast switching and record‑breaking optical gain paves the way for on‑chip, all‑optical circuitry capable of terahertz‑rate logic operations. When coupled with the recent advances in strong polariton‑polariton interactions observed in inorganic microcavities, such transistors could eventually operate with only a few photons, pushing switching energies into the attojoule regime.

A room‑temperature organic polariton transistor, Anton V. Zasedatelev, Anton V. Baranikov, Darius Urbonas, Fabio Scafirimuto, Ullrich Scherf, Thilo Stöferle, Rainer F. Mahrt & Pavlos G. Lagoudakis, Nature Photonics, volume 13, pages 378–383 (2019)