JQI-QuICS-CMTC Seminar

Applying a periodic Hamiltonian to a system of particles allows us to study out-of-equilibrium matter, like the prethermal discrete time crystal (PDTC). One can define a time-independent Hamiltonian that describes the dynamics of the driven system not continuously, but in a stroboscopic manner. This implies energy conservation during the validity window of this approximation.

This talk will introduce generalized Jordan–Wigner transformation on arbitrary triangulation of any simply connected manifold in 2d, 3d and general dimensions. This gives a duality between all fermionic systems and a new class of lattice gauge theories. This map preserves the locality and has an explicit dependence on the second Stiefel–Whitney class and a choice of spin structure on the manifold. In the spacetime picture, this mapping is exactly equivalent to introducing topological terms (Chern-Simon term in 2d or the Steenrod square term in general) to the Euclidean action.

We theoretically study the Hofstadter butterfly of a triangular network model in minimally twisted bilayer graphene. The band structure manifests periodicity in energy, mimicking that of Floquet systems. The butterfly diagrams provide fingerprints of the model parameters and reveal the hidden band topology. In a strong magnetic field, we establish that minimally twisted bilayer graphene realizes low-energy Floquet topological insulators (FTIs) carrying zero Chern number, while hosting chiral edge states in bulk gaps.

We propose a scheme to create electronic Floquet vortex states by irradiating the circularly-polarized laser light carrying non-zero orbital angular momentum on the two-dimensional semiconductor. We study the properties of the Floquet vortex states analytically and numerically using methods analogous to the techniques used for the analysis of superconducting vortex states, while we exhibit that the Floquet vortex created in the current system has the wider tunability.

We present an optimal protocol for encoding an unknown qubit state into a multiqubit Greenberger-Horne-Zeilinger-like state and, consequently, transferring quantum information in large systems exhibiting power-law (1/r^α) interactions. For all power-law exponents α between d and 2d+1, where d is the dimension of the system, the protocol yields a polynomial speedup for α>2d and a superpolynomial speedup for α≤2d, compared to the state of the art.

We finally made it to what seemed like sci-fi wishful thinking. Quantum computers are real and available on the cloud, and their power is growing at a greater-than-Moore’s-Law pace. What does this mean for those entering the job market soon? What will we be using these qubit-loaded behemoths for? Join us for some informal Q&A about this post-quantum era we find ourselves within.

Analog quantum algorithms are formulated in terms of Hamiltonians rather than unitary gates and include quantum adiabatic computing, quantum annealing, and the quantum approximate optimization algorithm (QAOA).  These algorithms are promising candidates for near-term quantum applications, but they often require fine tuning via the annealing schedule or variational parameters.  In this work we connect all these algorithms to the optimal analog procedure.  Notably, we explore how the optimal procedure approaches a smooth adiabatic procedure but with a superposed oscillatory pattern that can b

 Competition between unitary dynamics that scrambles quantum information non-locally and local measurements that probe and collapse the quantum state can result in a measurement induced entanglement phase transition. Here we study this phenomenon in an all-to-all Brownian hybrid circuit model of qubits that is analytically tractable. A part of the system is initially entangled with a reference which remains mixed at low measurement rates but is purified at high measurement rates.

The quantum beats are a well-understood phenomenon that has long been used as a spectroscopic technique in various systems. Here we demonstrate two new aspects in understanding and using quantum beats - (i) coupling to the electromagnetic vacuum allows for beating without an initial superposition between the excited levels, and (ii) by detecting the transmission in the forward direction in a superradiant burst, quantum beats can be collectively enhanced, increasing the signal strength useful in systems with low signal-to-noise.

Marcus is recognised as a principal contributor to the emergence of diamond-based quantum technologies, including quantum microscopy, quantum computing and quantum communications. These technologies represent new paradigms of microscopy, computing and communications that have the potential to revolutionise many disciplines of science and technology. During this seminar Marcus will share more about how the industry can expand the vision for quantum computing.
Zoom Link: https://umd.zoom.us/j/95285740962