The field of quantum science and technology is broad and crosses departments and faculties. Here at the Weizmann we have scientists working on the topic in the faculties of physics, chemistry, and mathematics and computer science (at the very least!). We are eager to learn about each other's work, find potential shared interests and initiate new collaborations.

The WIS-Q seminar (rhymes with NISQ...), aimed at being a discussion and meeting place for those of us at Weizmann who are interested in Quantum Science and Technology.

## Previous Talks

**Dr. Amit Finkler****Title:** Quantum Sensing**Abstract:**

The second quantum revolution relies on our ability to control and measure individual quantum states in micro- and nanoscopic systems, such as atoms, ions, and quantum dots. The techniques resulting from this capability may lead to a considerable improvement in several sensing modalities, for example atomic clocks and the measurement of magnetic fields on the nanoscale.

As an example for a quantum sensor, and of course after introducing the underlying concepts of quantum sensing, I will present the nitrogen-vacancy defect, or color center, in diamond. First, I will explain how one can use it to measure magnetic and electric fields, temperature, strain and even pH levels. Then, I will try to show what the "quantum advantage" that is possible in this class of sensors and will give a few examples from research activities in our group. Finally, I will also discuss several industrial applications, some of which are already in use or in development around the world.

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**Prof. Yuval Oreg
Titel**: Topological Superconductivity, Majorana fermions, and their Application to Quantum Computation

**Abstract**: A topological superconductor is a unique state of matter. Its non-Abelian variant has zero- energy excitations (or particles) known as the Majorana zero modes. These modes have emerged as a critical component for topological quantum computation. Similar to a classical ferromagnet state, in which the interactions between the spins suppress single spin fluctuations, the topological superconductor self-corrects errors in the qubit operations carried by the Majorana zero modes. This talk will briefly discuss the Majoranas' unique non- abelian character and how we can use them to achieve fault-tolerance quantum processing. We will describe how the Majorana zero modes emerge in topological superconductors, the current experimental progress in finding this unique state of matter in nature, and the strategies to address the challenges in its realization.

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**Prof. Barak Dayan
Titel**: Photonic Route to Fault-tolerant Quantum Computing

**Abstract**:

I will describe the photonic approach to quantum computation, which is the only technology that has been originally designed to reach the massive scaling required for fault- tolerant universal computation (> 10^6 physical qubits). It combines topological error correction and measurement-based quantum computation, with the leading effort relying on massive-scale silicon photonics.

I will then describe how cavity-QED with single atoms allows deterministic photon-atom two qubit gates, which in turn can drastically simplify the road towards fault-tolerant photonic quantum computing and improve its scaling to even larger numbers of physical qubits.

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**Prof. Zvika Brakerski
Titel**: How Quantum Computing is Changing Cryptography

**Abstract**:

It is fairly well known that Shor's algorithm for Factoring and Discrete Logarithm poses a challenge for cryptography in a quantum world. However, the implications of the viability of the quantum model on cryptography are much more profound, on a number of aspects. Naturally, it is harder to protect against quantum attackers than against classical ones, especially if the honest users remain classical. On the other hand, quantum computation and communication also present new tools that may assist in performing some cryptographic tasks. Further, the quantum model brings about new potential capabilities and cryptographic tasks that need to be explored, most basically the ability to prove that a potentially untrusted device indeed performs a quantum task.

In the talk I will explain how computer scientists, and in particular cryptographers, perceive the quantum computing model. I will discuss some of the fundamental questions that come up when the quantum model is incorporated into cryptography, such as the security of "lattice assumptions" against quantum attacks, the rewinding problem in cryptographic reductions, and the notion of semi-quantum cryptography which addresses questions in classical-quantum interaction.

No background in computer science or cryptography will be assumed.

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**Dr. Rotem Arnon-Friedman
Titel**: From “quantumness" certification to quantum cryptography and beyond

**Abstract**:

Imagine you enter a store that sells quantum key distribution systems (yes, they already exist). How do you know that the devices you buy are quantum? How do you know that they do what you want them to do? Should you use them even if you don’t trust the manufacturer? In this talk, I will present the concept of “quantumness” certification in its strongest form and discuss the work done in our group to use it to prove the security of various quantum cryptographic protocols. I will then argue that taking a similar point of view as in the cryptographic setup is relevant for many topics, from quantum computation to condensed matter physics.

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**Prof. Roee Ozeri
Title**: Trapped ions quantum computing – a tale of highly social qubits

**Abstract**:

In this talk I will review the basic methods and the current state-of-the-art in trapped ion quantum computing and compare the advantages and disadvantages of this to other QC technologies. I will further describe the progress towards building the WeizQC - a trapped ion quantum computer at the Weizmann Institute of Science. In the second part of the talk I will describe one unique feature of trapped-ion qubits: their all-to- all connectivity. I will describe methods that use this connectivity to engineer multi-qubit gates and operations. Multi-qubit gates have many advantages, both for near term noisy quantum computers, as well as for achieving fault- tolerance. As an example I will show that using multi-qubit gates, the threshold for fault-tolerant quantum computing can be enlarged and the ratio of logical to physical qubit error reduced.

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**Prof. Erez Berg
Title**: Computing the Quantum: Classical and Quantum Simulations of Many-Body Systems

**Abstract**:

Many problems of interest, ranging from condensed matter physics and quantum chemistry to quantum information, require finding the ground state of a system of many interacting degrees of freedom (e.g., qubits or quantum spins). The main challenge stems from the exponential scaling of the Hilbert space dimension with the number of qubits. I will first discuss various strategies to tackle this problem using classical computers, such as tensor network states and Monte Carlo sampling, and their limitations. Quantum computers are ideally suited for this task; I will present a proposal to simulate quantum systems on noisy intermediate-scale quantum (NISQ) devices made of imperfect qubits, where the noise level translates into a finite energy density (i.e., finite temperature).

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**Prof. Ofer Firstenberg
Tilte**: Quantum Interfaces between Photons & Atoms

**Abstract**:

For a long time, humankind has aspired to exchange information between flying qubits – photons – and long-lived matter qubits – such as atoms. This reversible exchange is needed in any setup of a quantum network: for quantum memories, repeaters for long-distance quantum communication, and distributed quantum computing. Moreover, coupling photons to atoms enables indirect photon-photon interaction that can implement deterministic entanglement sources and photonic quantum gates. We will explain the basic principles underlying light-matter interfaces, their realization with atomic gases in our lab, and our (exciting) plans to create efficient “quantum antennas” with atomic arrays.

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**Dr. Serge Rosenblum
Title**: Superconducting Quantum Computing

**Abstract**:

In this talk, we will explore one of the leading technologies for quantum computing: superconducting circuits. This is the

technology used by Google, IBM and many others to build their quantum computers. We will start by reviewing the underlying principles and the current status of this technology. Then, we will discuss the research done in our lab at the condensed matter department at WIS— from the fabrication of our chips to how we encode quantum information in microwave resonators. We will use our novel approach for creating superconducting qubits to correct errors and bring the qubits to a new regime of quantum coherence. Preliminary data of our progress towards this goal will be presented.

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