Friday Quantum Seminar

Instabilities, where initially small fluctuations seed the formation of large-scale structures, govern the dynamics in various fluid flows. The Rayleigh-Taylor instability (RTI) is an iconic example that leads to the development of mushroom-shaped incursions when immiscible fluids are accelerated into each other. RTI drives structure formation throughout science and engineering including table-top oil and water mixtures; supernova explosions; and inertial confinement fusion.  Despite its ubiquity, controlled laboratory RTI experiments are technically challenging.

Abstract: Instabilities, where initially small fluctuations seed the formation of large-scale structures, govern the dynamics in various fluid flows. The Rayleigh-Taylor instability (RTI) is an iconic example that leads to the development of mushroom-shaped incursions when immiscible fluids are accelerated into each other. RTI drives structure formation throughout science and engineering including table-top oil and water mixtures; supernova explosions; and inertial confinement fusion.  Despite its ubiquity, controlled laboratory RTI experiments are technically challenging.

We extend entropy production to a deeply quantum regime involving noncommuting conserved quantities. Consider a unitary transporting conserved quantities (“charges”) between two systems initialized in thermal states. Three common formulae model the entropy produced. They respectively cast entropy as an extensive thermodynamic variable, as an information-theoretic uncertainty measure, and as a quantifier of irreversibility. Often, the charges are assumed to commute with each other (e.g., energy and particle number). Yet quantum charges can fail to commute.

Abstract: We extend entropy production to a deeply quantum regime involving noncommuting conserved quantities. Consider a unitary transporting conserved quantities (“charges”) between two systems initialized in thermal states. Three common formulae model the entropy produced. They respectively cast entropy as an extensive thermodynamic variable, as an information-theoretic uncertainty measure, and as a quantifier of irreversibility. Often, the charges are assumed to commute with each other (e.g., energy and particle number). Yet quantum charges can fail to commute.

Abstract: In this talk, I present an experimental realization of a quantum absorption refrigerator formed from superconducting circuits. The refrigerator is used to reset a transmon qubit to a temperature lower than that achievable with any one available bath. The process is driven by a thermal gradient and is autonomous -- requires no external control. The refrigerator exploits an engineered three-body interaction between the target qubit and two auxiliary qudits coupled to thermal environments, formed from microwave waveguides populated with thermal photons.

In this talk, I present an experimental realization of a quantum absorption refrigerator formed from superconducting circuits. The refrigerator is used to reset a transmon qubit to a temperature lower than that achievable with any one available bath. The process is driven by a thermal gradient and is autonomous -- requires no external control. The refrigerator exploits an engineered three-body interaction between the target qubit and two auxiliary qudits coupled to thermal environments, formed from microwave waveguides populated with thermal photons.

We introduce parallel-sequential (PS) circuits, a family of quantum circuits characterized by a tunable degree of entanglement and maximum correlation length, which interpolates between brickwall and sequential circuits. We provide evidence that on noisy devices, properly chosen PS circuits suppress error proliferation and exhibit superior trainability and evaluation accuracy when employed as variational circuits, thus outperforming brickwall, sequential, and log-depth circuits in [Malz*, Styliaris*, Wei*, Cirac, PRL 2024] across most parameter regimes.

Abstract: We introduce parallel-sequential (PS) circuits, a family of quantum circuits characterized by a tunable degree of entanglement and maximum correlation length, which interpolates between brickwall and sequential circuits. We provide evidence that on noisy devices, properly chosen PS circuits suppress error proliferation and exhibit superior trainability and evaluation accuracy when employed as variational circuits, thus outperforming brickwall, sequential, and log-depth circuits in [Malz*, Styliaris*, Wei*, Cirac, PRL 2024] across most parameter regimes.

Quantum sensing extends the vast benefits of a quantum advantage to traditional metrology.  A common method of quantum sensing utilizes coherent, crystal defects in semi-conductors (such as nitrogen vacancy centers in diamond) to perform high-precision measurements on a variety of length scales.  Such measurements might span from vectorized magnetometry of macroscopic computer chips to nanoscale strain or temperature mapping in a target matrial.  In exploring new regimes for quantum sensing, we need to model and assess their viability through theoretical or simula

Arrays of gate-defined semiconductor quantum dots are among the leading candidates for building scalable quantum processors.  High-fidelity initialization, control, and readout of spin qubit registers require exquisite and targeted control over key Hamiltonian parameters that define the electrostatic environment.  However, due to the tight gate pitch, capacitive crosstalk between gates hinders independent tuning of chemical potentials and interdot couplings.  While virtual gates offer a practical solution, determining all the required cross-capacitance matrices accurate