Hafezi Research Group

Topological protection allows realization of integrated photonic devices that are robust against certain fabrication-induced disorder. However, it is usually challenging to achieve device reconfigurability along with topological robustness. We recently proposed the design of reconfigurable topological photonic device using anomalous Hall effect.

The topological phases of matter are characterized using the Berry phase, a geometrical phase associated with the energy-momentum band structure. The quantization of the Berry phase and the associated wavefunction polarization manifest as remarkably robust physical observables, such as quantized Hall conductivity and disorder-insensitive photonic transport. Recently, a novel class of topological phases, called higher-order topological phases, were proposed by generalizing the fundamental relationship between the Berry phase and quantized polarization, from dipole to multipole moments.

Researchers at the Joint Quantum Institute (JQI) have created the first silicon chip that can reliably constrain light to its four corners. The effect, which arises from interfering optical pathways, isn't altered by small defects during fabrication and could eventually enable the creation of robust sources of quantum light. That robustness is due to topological physics, which describes the properties of materials that are insensitive to small changes in geometry. The cornering of light, which was reported June 17 in Nature Photonics, is a realization of a new topological effect, first predicted in 2017.

JQI Fellow Mohammad Hafezi has been named a finalist for the 2019 Blavatnik National Awards for Young Scientists.He is one of 31 researchers competing for three Blavatnik National Laureate Awards in the categories of Physical Sciences and Engineering, Chemistry and Life Sciences, and is one of 10 finalists in Physical Sciences and Engineering. Each of the three National Laureates will win $250,000—the world’s largest unrestricted prize for early-career scientists. The awards are sponsored by the Blavatnik Family Foundation and the New York Academy of Sciences.

 A quantum light source has many potential applications in quantum information sciences. However, any on-chip realization is marred by the nanofabrication-induced disorder. We recently demonstrated the first topological source of quantum light where the generated photons are robustly generated and less affected by disorder. Our results were published in Nature.  

The smallest amount of light you can have is one photon, so dim that it’s pretty much invisible to humans. While imperceptible, these tiny blips of energy are useful for carrying quantum information around. Ideally, every quantum courier would be the same, but there isn’t a straightforward way to produce a stream of identical photons. This is particularly challenging when individual photons come from fabricated chips. Now, researchers at the Joint Quantum Institute (JQI) have demonstrated a new approach that enables different devices to repeatedly emit nearly identical single photons. The team, led by JQI Fellow Mohammad Hafezi, made a silicon chip that guides light around the device’s edge, where it is inherently protected against disruptions. Previously, Hafezi and colleagues showed that this design can reduce the likelihood of optical signal degradation. In a paper published online on Sept. 10 in Nature, the team explains that the same physics which protects the light along the chip’s edge also ensures reliable photon production.

We reduce measurement errors in a quantum computer using machine learning techniques. We exploit a simple yet versatile neural network to classify multi-qubit quantum states, which is trained using experimental data. This flexible approach allows the incorporation of any number of features of the data with minimal modifications to the underlying network architecture. We experimentally illustrate this approach in the readout of trapped-ion qubits using additional spatial and temporal features in the data.

In a recent Feature Article in Optics and Photonics News of OSA, we review the basic concepts in topological photonics and recent developments in the field. The goal was to make it accessible to a wide audience.

Engineering phonon transport in physical systems is a subject of interest in the study of materials, and plays a crucial role in controlling energy and heat transfer. Of particular interest are non-reciprocal phononic systems, which in direct analogy to electric diodes, provide a directional flow of energy. Here, we propose an engineered nanostructured material, in which tunable non-reciprocal phonon transport is achieved through optomechanical coupling. Our scheme relies on breaking time-reversal symmetry by a spatially varying laser drive, which manipulates low-energy acoustic phonons.

Optical highways for light are at the heart of modern communications. But when it comes to guiding individual blips of light called photons, reliable transit is far less common. Now, a collaboration of researchers from the Joint Quantum Institute (JQI), led by JQI Fellows Mohammad Hafezi and Edo Waks, has created a photonic chip that both generates single photons, and steers them around. The device, described in the Feb. 9 issue of Science, features a way for the quantum light to seamlessly move, unaffected by certain obstacles.