Publications (61)
Evaluating the noise resilience of variational quantum algorithms
Enrico Fontana, Nathan Fitzpatrick, David Muñoz Ramo +2
We simulate the effects of different types of noise in state preparation circuits of variational quantum algorithms. We first use a variational quantum eigensolver to find the grou…
Femtosecond spin current pulses generated by the non-thermal spin-dependent Seebeck effect and interacting with ferromagnets in spin valves
Alexandr Alekhin, Ilya Razdolski, Nikita Ilin +8
Using the sensitivity of magneto-induced second harmonic generation to spin currents (SC), we demonstrate in Fe/Au/Fe/MgO(001) pseudo spin valves the generation of 250 fs-long SC p…
Current-induced energy barrier suppression for electromigration from first principles
Ruoxing Zhang, Ivan Rungger, Stefano Sanvito +1
We present an efficient method for evaluating current-induced forces in nanoscale junctions, which naturally integrates into the non-equilibrium Green's function formalism implemen…
The DFT+ method for electron correlation effects at transition metal surfaces
Andrea Droghetti, MiloÅ¡ M. RadonjiÄ, Anita Halder +2
We present a computational approach for electronically correlated metallic surfaces and interfaces, which combines Density Functional and Dynamical Mean Field Theory using a multi-…
Pressure induced electronic transitions in Samarium monochalcogenides
Debalina Banerjee, Evgeny Plekhanov, Ivan Rungger +1
Pressure induced isostructural insulator to metal transition for SmS is characterised by the presence of an intermediate valence state at higher pressure which cannot be captured b…
Search for alternative magnetic tunnel junctions based on all-Heusler stacks
Worasak Rotjanapittayakul, Jariyanee Prasongkit, Ivan Rungger +3
By imposing the constraints of structural compatibility, stability and a large tunneling magneto-resistance, we have identified the FeAl/BiF/FeAl stack as a possible al…
Oxygen modulated quantum conductance for ultra-thin HfO-based memristive switching devices
Xiaoliang Zhong, Ivan Rungger, Peter Zapol +1
Memristive switching devices, candidates for resistive random access memory technology, have been shown to switch off through a progression of states with quantized conductance and…
Encoding optimization for quantum machine learning demonstrated on a superconducting transmon qutrit
Shuxiang Cao, Weixi Zhang, Jules Tilly +9
Qutrits, three-level quantum systems, have the advantage of potentially requiring fewer components than the typically used two-level qubits to construct equivalent quantum circuits…
Unique excitonic effects in tungsten disulphide monolayers on two-layer graphene
Cristina E. Giusca, Ivan Rungger, Vishal Panchal +8
Light emission in atomically thin heterostructures is known to depend on the type of materials, number and stacking sequence of the constituent layers. Here we show that the thickn…
A fault-tolerant variational quantum algorithm with limited T-depth
Hasan Sayginel, Francois Jamet, Abhishek Agarwal +2
We propose a variational quantum eigensolver (VQE) algorithm that uses a fault-tolerant gate-set, and is hence suitable for implementation on a future error-corrected quantum compu…
Accurate self-energy algorithm for quasi-1D systems
Ivan Rungger, Stefano Sanvito
We present a complete prescription for the numerical calculation of surface Green's functions and self-energies of semi-infinite quasi-onedimensional systems. Our work extends the…
Quantum transport simulation scheme including strong correlations and its application to organic radicals adsorbed on gold
Andrea Droghetti, Ivan Rungger
We present a computational method to quantitatively describe the linear-response conductance of nanoscale devices in the Kondo regime. This method relies on a projection scheme to…
Emulating two qubits with a four-level transmon qudit for variational quantum algorithms
Shuxiang Cao, Mustafa Bakr, Giulio Campanaro +7
Using quantum systems with more than two levels, or qudits, can scale the computation space of quantum processors more efficiently than using qubits, which may offer an easier phys…
Spin-Polarized Tunneling through Chemical Vapor Deposited Multilayer Molybdenum Disulfide
André Dankert, Parham Pashaei, M. Venkata Kamalakar +10
The two-dimensional (2D) semiconductor molybdenum disulfide (MoS2) has attracted widespread attention for its extraordinary electrical, optical, spin and valley related properties.…
Anderson impurity solver integrating tensor network methods with quantum computing
Francois Jamet, Lachlan P. Lindoy, Yannic Rath +6
Solving the Anderson impurity model typically involves a two-step process, where one first calculates the ground state of the Hamiltonian, and then computes its dynamical propertie…
Modelling non-Markovian noise in driven superconducting qubits
Abhishek Agarwal, Lachlan P. Lindoy, Deep Lall +2
Non-Markovian noise can be a significant source of errors in superconducting qubits. We develop gate sequences utilising mirrored pseudoidentities that allow us to characterise and…
A non-equilibrium quantum transport framework for spintronic devices with dynamical correlations
Declan Nell, Milos Radonjic, Ivan Rungger +3
Two-terminal spintronic devices remain challenging to model under realistic operating conditions, where the interplay of complex electronic structures, correlation effects and bias…
The Variational Quantum Eigensolver: a review of methods and best practices
Jules Tilly, Hongxiang Chen, Shuxiang Cao +8
The variational quantum eigensolver (or VQE) uses the variational principle to compute the ground state energy of a Hamiltonian, a problem that is central to quantum chemistry and…
Dynamical Decoupling using Universal Optimal Tracking
Amit Devra, Emanuel Malvetti, Niklas J. Glaser +7
Dynamical decoupling (DD) is a widely used and resource-efficient technique for error suppression, but conventional DD relies on periodically repeating a short pulse block to refoc…
Large bias-dependent magnetoresistance in all-oxide magnetic tunnel junctions with a ferroelectric barrier
Nuala M. Caffrey, Thomas Archer, Ivan Rungger +1
All-oxide magnetic tunnel junctions (MTJs) incorporating functional materials as insulating barriers have the potential of becoming the founding technology for novel multi-function…
Efficient spin injection and giant magnetoresistance in Fe/MoS/Fe junctions
Kapildeb Dolui, Awadhesh Narayan, Ivan Rungger +1
We demonstrate giant magnetoresistance in Fe/MoS/Fe junctions by means of \textit{ab-initio} transport calculations. We show that junctions incorporating either a mono- or a bi…
Resonant electronic states and I-V curves of Fe/MgO/Fe(100) tunnel junctions
Ivan Rungger, Oleg N. Mryasov, Stefano Sanvito
The bias dependence of the tunnel magnetoresistance (TMR) of Fe/MgO/Fe tunnel junctions is investigated theoretically with a fully self-consistent scheme that combines the non-equi…
Fast-tracking and disentangling of qubit noise fluctuations using minimal-data averaging and hierarchical discrete fluctuation auto-segmentation
Abhishek Agarwal, Lachlan P. Lindoy, Deep Lall +3
Qubit noise and fluctuations of the noise over time are key factors limiting the performance of quantum computers. Characterising them with high temporal resolution is challenging…
Spin-orbit induced equilibrium spin currents in materials
Andrea Droghetti, Ivan Rungger, Angel Rubio +1
The existence of spin-currents in absence of any driving external fields is commonly considered an exotic phenomenon appearing only in quantum materials, such as topological insula…
Efficient characterization of qudit logical gates with gate set tomography using an error-free Virtual-Z-gate model
Shuxiang Cao, Deep Lall, Mustafa Bakr +7
Gate-set tomography (GST) characterizes the process matrix of quantum logic gates, along with measurement and state preparation errors in quantum processors. GST typically requires…
Ab initio study on the magneto-structural properties of MnAs
Ivan Rungger, Stefano Sanvito
The magnetic and structural properties of MnAs are studied with ab initio methods, and by mapping total energies onto a Heisenberg model. The stability of the different phases is f…
Krylov variational quantum algorithm for first principles materials simulations
Francois Jamet, Abhishek Agarwal, Carla Lupo +3
We propose an algorithm to obtain Green's functions as a continued fraction on quantum computers, which is based on the construction of the Krylov basis using variational quantum a…
Robust organic radical molecular junctions using acetylene terminated groups for C-Au bond formation
Francesc Bejarano, Ignacio Jose Olavarria-Contreras, Andrea Droghetti +9
Organic paramagnetic and electroactive molecules are attracting interest as core components of molecular electronic and spintronic devices. Currently, further progress is hindered…
pyTTN: An Open Source Toolbox for Open and Closed System Quantum Dynamics Simulations Using Tree Tensor Networks
Lachlan P Lindoy, Daniel Rodrigo-Albert, Yannic Rath +1
We present the Python Tree Tensor Network package (pyTTN) for the evaluation of dynamical properties of closed and open quantum systems that makes use of Tree Tensor Network (TTN),…
Efficient recovery of variational quantum algorithms landscapes using classical signal processing
Enrico Fontana, Ivan Rungger, Ross Duncan +1
We employ spectral analysis and compressed sensing to identify settings where a variational algorithm's cost function can be recovered purely classically or with minimal quantum co…
Electronic Transport Through EuO Spin Filter Tunnel Junctions
Nuttachai Jutong, Ivan Rungger, Cosima Schuster +3
Epitaxial spin filter tunnel junctions based on the ferromagnetic semiconductor europium monoxide, EuO, are investigated by means of density functional theory. In particular, we fo…
Effect of dynamical electron correlations on the tunnelling magnetoresistance of Fe/MgO/Fe(001) junctions
Declan Nell, Stefano Sanvito, Ivan Rungger +1
We employ dynamical mean-field theory (DMFT) combined with density functional theory (DFT) and the non-equilibrium Green's function technique to investigate the steady-state transp…
A Langevin sampler for quantum tomography
Tameem Adel, Abhishek Agarwal, Stéphane Chrétien +4
Quantum tomography involves obtaining a full classical description of a prepared quantum state from experimental results. We propose a Langevin sampler for quantum tomography, that…
Structural Origins of Conductance Fluctuations in Gold-Thiolate Molecular Transport Junctions
William R. French, Christopher R. Iacovella, Ivan Rungger +3
We report detailed atomistic simulations combined with high-fidelity conductance calculations to probe the structural origins of conductance fluctuations in thermally evolving Au-b…
Variational preparation of normal matrix product states on quantum computers
Ben Jaderberg, George Pennington, Kate V. Marshall +6
Preparing matrix product states (MPSs) on quantum computers is an essential routine in the simulation of many-body physics. However, widely-used schemes based on staircase circuits…
Spectral analysis for noise diagnostics and filter-based digital error mitigation
Enrico Fontana, Ivan Rungger, Ross Duncan +1
We investigate the effects of noise on parameterised quantum circuits using spectral analysis and classical signal processing tools. For different noise models, we quantify the add…
Origin of the n-type and p-type conductivity of MoS2 monolayers on a SiO2 substrate
Kapildeb Dolui, Ivan Rungger, Stefano Sanvito
Ab-initio density functional theory calculations are performed to study the electronic properties of a MoS2 monolayer deposited over a SiO2 substrate in the presence of interface i…
Stretching of BDT-gold molecular junctions: thiol or thiolate termination?
Amaury de Melo Souza, Ivan Rungger, Renato Borges Pontes +4
It is often assumed that the hydrogen atoms in the thiol groups of a benzene-1,4-dithiol dissociate when Au-benzene-1,4-dithiol-Au junctions are formed. We demonstrate, by stabilit…
Non-trivial symmetries in quantum landscapes and their resilience to quantum noise
Enrico Fontana, M. Cerezo, Andrew Arrasmith +2
Very little is known about the cost landscape for parametrized Quantum Circuits (PQCs). Nevertheless, PQCs are employed in Quantum Neural Networks and Variational Quantum Algorithm…
Dynamical Mean-Field Theory for spin-dependent electron transport in spin-valve devices
Andrea Droghetti, Milos M. RadonjiÄ, Liviu Chioncel +1
We present the combination of Density Functional Theory (DFT) and Dynamical Mean Field Theory (DMFT) for computing the electron transmission through two-terminals nanoscale devices…
Data-Driven Dynamical Mean-Field Theory: an error-correction approach to solve the quantum many-body problem using machine learning
Evan Sheridan, Christopher Rhodes, Francois Jamet +2
Machine learning opens new avenues for modelling correlated materials. Quantum embedding approaches, such as the dynamical mean-field theory (DMFT), provide corrections to first-pr…
Topological surface states scattering in Antimony
Awadhesh Narayan, Ivan Rungger, Stefano Sanvito
In this work we study the topologically protected states of the Sb(111) surface by using ab-initio transport theory. In the presence of a strong surface perturbation we obtain stan…
Spin-valve Effect in NiFe/MoS2/NiFe Junctions
Weiyi Wang, Awadhesh Narayan, Lei Tang +8
Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have been recently proposed as appealing candidate materials for spintronic applications owing to their distinc…
Phenomenology of Andreev reflection from first-principles transport theory
Awadhesh Narayan, Ivan Rungger, Stefano Sanvito
We study Andreev reflection in normal metal-superconductor junctions by using an extended Blonder-Tinkham-Klapwijk model combined with transport calculations based on density funct…
Atomistic Simulations of Highly Conductive Molecular Transport Junctions Under Realistic Conditions
William R. French, Christopher R. Iacovella, Ivan Rungger +3
We report state-of-the-art atomistic simulations combined with high-fidelity conductance calculations to probe structure-conductance relationships in Au-benzenedithiolate(BDT)-Au j…
Existence of Shapiro Steps in the Dissipative Regime in Superconducting Weak Links
Connor D. Shelly, Patrick See, Ivan Rungger +1
We present measurements of microwave-induced Shapiro steps in a superconducting nanobridge weak link in the dissipative branch of a hysteretic current-voltage characteristic. We de…
Quantum State Discrimination Using Noisy Quantum Neural Networks
Andrew Patterson, Hongxiang Chen, Leonard Wossnig +3
Near-term quantum computers are noisy, and therefore must run algorithms with a low circuit depth and qubit count. Here we investigate how noise affects a quantum neural network (Q…
Gate control of spin-polarized conductance in alloyed transition metal nano-contacts
Ilia N. Sivkov, Oleg O. Brovko, Ivan Rungger +1
To date, endeavors in nanoscale spintronics are dominated by the use of single-electron or single-spin transistors having at their heart a semiconductor, metallic or molecular quan…
Electronic and magnetic properties of Ti4O7 predicted by self-interaction corrected density functional theory
Xiaoliang Zhong, Ivan Rungger, Peter Zapol +1
Understanding electronic properties of sub-stoichiometric phases of titanium oxide such as Magnéli phase Ti4O7 is crucial in designing and modeling resistive switching devices. He…
Coexistance of giant tunneling electroresistance and magnetoresistance in an all-oxide magnetic tunnel junction
Nuala Mai Caffrey, Thomas Archer, Ivan Rungger +1
We demonstrate with first-principles electron transport calculations that large tunneling magnetoresistance (TMR) and tunneling electroresistance (TER) effects can coexist in an al…
QCalEval: Benchmarking Vision-Language Models for Quantum Calibration Plot Understanding
Shuxiang Cao, Zijian Zhang, Abhishek Agarwal +29
Quantum computing calibration depends on interpreting experimental data, and calibration plots provide the most universal human-readable representation for this task, yet no system…
A Review and Collection of Metrics and Benchmarks for Quantum Computers: definitions, methodologies and software
Deep Lall, Abhishek Agarwal, Weixi Zhang +15
Quantum computers have the potential to provide an advantage over classical computers in a number of areas. Numerous metrics to benchmark the performance of quantum computers, rang…
Quantum subspace expansion algorithm for Green's functions
Francois Jamet, Abhishek Agarwal, Ivan Rungger
We present an algorithm to compute Green's functions on quantum computers for interacting electron systems, which is a challenging task on conventional computers. It uses a continu…
Ab-initio study on the possible doping strategies for MoS monolayers
Kapildeb Dolui, Ivan Rungger, Chaitanya Das Pemmaraju +1
Density functional theory is used to systematically study the electronic and magnetic properties of doped MoS monolayers, where the dopants are incorporated both via S/Mo subst…
Reduced Density Matrix Sampling: Self-consistent Embedding and Multiscale Electronic Structure on Current Generation Quantum Computers
Jules Tilly, P. V. Sriluckshmy, Akashkumar Patel +6
We investigate fully self-consistent multiscale quantum-classical algorithms on current generation superconducting quantum computers, in a unified approach to tackle the correlated…
First-principles spin-transfer torque in CuMnAsGaPCuMnAs junctions
Maria Stamenova, Razie Mohebbi, Jamileh Seyedyazdi +2
We demonstrate that an all-antiferromagnetic tunnel junction with current perpendicular to the plane geometry can be used as an efficient spintronics device with potential high fre…
Quantum subspace expansion approach for simulating dynamical response functions of Kitaev spin liquids
Chukwudubem Umeano, François Jamet, Lachlan P. Lindoy +2
We develop a quantum simulation-based approach for studying properties of strongly correlated magnetic materials at increasing scale. We consider a paradigmatic example of a quantu…
Ab-initio transport across Bismuth Selenide surface barriers
Awadhesh Narayan, Ivan Rungger, Andrea Droghetti +1
We investigate the effect of potential barriers in the form of step edges on the scattering properties of BiSe(111) topological surface states by means of large-scale ab-in…
Single atom anisotropic magnetoresistance on a topological insulator surface
Awadhesh Narayan, Ivan Rungger, Stefano Sanvito
We demonstrate single atom anisotropic magnetoresistance on the surface of a topological insulator, arising from the interplay between the helical spin-momentum-locked surface elec…
Classical simulations of noisy variational quantum circuits
Enrico Fontana, Manuel S. Rudolph, Ross Duncan +2
Noise detrimentally affects quantum computations so that they not only become less accurate but also easier to simulate classically as systems scale up. We construct a classical si…
Maximally Localized Dynamical Quantum Embedding for Solving Many-Body Correlated Systems
Carla Lupo, François Jamet, Terence Tse +2
We present a quantum embedding methodology to resolve the Anderson impurity model in the context of dynamical mean-field theory, based on an extended exact diagonalization method.…