Entangled Quantum Memristors

  1. Shubham Kumar,
  2. Francisco A. Cárdenas-López,
  3. Narendra N. Hegade,
  4. Xi Chen,
  5. Francisco Albarrán-Arriagada,
  6. Enrique Solano,
  7. and Gabriel Alvarado Barrios
We propose the interaction of two quantum memristors via capacitive and inductive coupling in feasible superconducting circuit architectures. In this composed system the input gets
correlated in time, which changes the dynamic response of each quantum memristor in terms of its pinched hysteresis curve and their nontrivial entanglement. In this sense, the concurrence and memristive dynamics follow an inverse behavior, showing maximal values of entanglement when the hysteresis curve is minimal and vice versa. Moreover, the direction followed in time by the hysteresis curve is reversed whenever the quantum memristor entanglement is maximal. The study of composed quantum memristors paves the way for developing neuromorphic quantum computers and native quantum neural networks, on the path towards quantum advantage with current NISQ technologies.

Challenges in Open-air Microwave Quantum Communication and Sensing

  1. Mikel Sanz,
  2. Kirill G. Fedorov,
  3. Frank Deppe,
  4. and Enrique Solano
Quantum communication is a holy grail to achieve secure communication among a set of partners, since it is provably unbreakable by physical laws. Quantum sensing employs quantum entanglement
as an extra resource to determine parameters by either using less resources or attaining a precision unachievable in classical protocols. A paradigmatic example is the quantum radar, which allows one to detect an object without being detected oneself, by making use of the additional asset provided by quantum entanglement to reduce the intensity of the signal. In the optical regime, impressive technological advances have been reached in the last years, such as the first quantum communication between ground and satellites, as well as the first proof-of-principle experiments in quantum sensing. The development of microwave quantum technologies turned out, nonetheless, to be more challenging. Here, we will discuss the challenges regarding the use of microwaves for quantum communication and sensing. Based on this analysis, we propose a roadmap to achieve real-life applications in these fields.

Lattice gauge fields via modulation in circuit QED: The bosonic Creutz ladder

  1. Hadiseh Alaeian,
  2. Chung Wai Sandbo Chang,
  3. Mehran Vahdani Moghaddam,
  4. Christopher M. Wilson,
  5. Enrique Solano,
  6. and Enrique Rico
In this work we propose two protocols to make an effective gauge potential for microwave photons in circuit QED. The schemes consist of coupled transmons whose flux are harmonically
modulated in time. We investigate the effect of various types of capacitive and inductive couplings, and the role of the fixed phase offset of each site on the complex coupling rate between coupled qubits. These configurations can be directly realised in a superconducting circuit and is easily extendable to a scalable lattice. Due to the intrinsic non-linearity of the transmon qubits such lattices would be an ideal platform for simulating Bose-Hubbard Hamiltonians with non-trivial gauge fields.

Digital-Analog Quantum Simulations with Superconducting Circuits

  1. Lucas Lamata,
  2. Adrian Parra-Rodriguez,
  3. Mikel Sanz,
  4. and Enrique Solano
Quantum simulations consist in the intentional reproduction of physical or unphysical models into another more controllable quantum system. Beyond establishing communication vessels
between unconnected fields, they promise to solve complex problems which may be considered as intractable for classical computers. From a historic perspective, two independent approaches have been pursued, namely, digital and analog quantum simulations. The former usually provide universality and flexibility, while the latter allows for scalability. Here, we review recent literature merging both paradigms in the context of superconducting circuits, yielding: digital-analog quantum simulations. In this manner, we aim at getting the best of both approaches in the most advanced quantum platform involving superconducting qubits and microwave transmission lines. The discussed merge of quantum simulation concepts, digital and analog, may open the possibility in the near future for outperforming classical computers in relevant problems, enabling the reach of quantum supremacy.

Divergence-free multi-mode circuit quantum electrodynamics

  1. Mario F. Gely,
  2. Adrian Parra-Rodriguez,
  3. Daniel Bothner,
  4. Ya. M. Blanter,
  5. Sal J. Bosman,
  6. Enrique Solano,
  7. and Gary A. Steele
Circuit quantum electrodynamics studies the interaction of artificial atoms and electromagnetic modes constructed from superconducting circuitry. While the theory of an atom coupled
to one mode of a resonator is well studied, considering multiple modes leads to divergences which are not well understood. Here, we introduce a full quantum model of a multi-mode resonator coupled to a Josephson junction atom. Using circuit quantization, we find a Hamiltonian in which parameters of the atom are naturally renormalized as additional modes are considered. In our model, we circumvent the divergence problem, and its formulation reveals a physical understanding of the mechanisms of convergence in ubiquitous models in circuit quantum electrodynamics.

Superluminal Physics with Superconducting Circuit Technology

  1. Carlos Sabín,
  2. Borja Peropadre,
  3. Lucas Lamata,
  4. and Enrique Solano
We introduce a toolbox for the quantum simulation of superluminal motion with superconducting circuits. We show that it is possible to simulate the motion of a superconducting qubit
at constant velocities that exceed the speed of light in the electromagnetic medium and the subsequent emission of Ginzburg radiation. We consider as well possible setups for simulating the superluminal motion of a mirror, finding a link with the superradiant phase transition of the Dicke model.

Approximate Quantum Adders with Genetic Algorithms: An IBM Quantum Experience

  1. Rui Li,
  2. Unai Alvarez-Rodriguez,
  3. Lucas Lamata,
  4. and Enrique Solano
It has been proven that quantum adders are forbidden by the laws of quantum mechanics. We analyze theoretical proposals for the implementation of approximate quantum adders and optimize
them by means of genetic algorithms, improving previous protocols in terms of efficiency and fidelity. Furthermore, we experimentally realize a suitable approximate quantum adder with the cloud quantum computing facilities provided by IBM Quantum Experience. The development of approximate quantum adders enhances the toolbox of quantum information protocols, paving the way for novel applications in quantum technologies.

Entanglement of superconducting qubits via acceleration radiation

  1. Laura García-Álvarez,
  2. Simone Felicetti,
  3. Enrique Rico,
  4. Enrique Solano,
  5. and Carlos Sabín
We show that simulated relativistic motion can generate entanglement between artificial atoms and protect them from spontaneous emission. We consider a pair of superconducting qubits
coupled to a resonator mode, where the modulation of the coupling strength can mimic the harmonic motion of the qubits at relativistic speeds, generating acceleration radiation. We find the optimal feasible conditions for generating a stationary entangled state between the qubits when they are initially prepared in their ground state. Furthermore, we analyze the effects of motion on the probability of spontaneous emission in the standard scenarios of single-atom and two-atom superradiance, where one or two excitations are initially present. Finally, we show that relativistic motion induces sub-radiance and can generate a Zeno-like effect, preserving the excitations from radiative decay.

Few-qubit quantum-classical simulation of strongly correlated lattice fermions

  1. Juha M Kreula,
  2. Laura García-Álvarez,
  3. Lucas Lamata,
  4. Stephen R Clark,
  5. Enrique Solano,
  6. and Dieter Jaksch
We study a proof-of-principle example of the recently proposed hybrid quantum-classical simulation of strongly correlated fermion models in the thermodynamic limit. In a „two-site“
dynamical mean-field theory (DMFT) approach we reduce the Hubbard model to an effective impurity model subject to self-consistency conditions. The resulting minimal two-site representation of the non-linear hybrid setup involves four qubits implementing the impurity problem, plus an ancilla qubit on which all measurements are performed. We outline a possible implementation with superconducting circuits feasible with near-future technology.

Spin-boson model with an engineered reservoir in circuit quantum electrodynamics

  1. Max Haeberlein,
  2. Frank Deppe,
  3. Andreas Kurcz,
  4. Jan Goetz,
  5. Alexander Baust,
  6. Peter Eder,
  7. Kirill Fedorov,
  8. Michael Fischer,
  9. Edwin P. Menzel,
  10. Manuel J. Schwarz,
  11. Friedrich Wulschner,
  12. Edwar Xie,
  13. Ling Zhong,
  14. Enrique Solano,
  15. Achim Marx,
  16. Juan José García-Ripoll,
  17. and Rudolf Gross
A superconducting qubit coupled to an open transmission line represents an implementation of the spin-boson model with a broadband environment. We show that this environment can be
engineered by introducing partial reflectors into the transmission line, allowing to shape the spectral function, J({\omega}), of the spin-boson model. The spectral function can be accessed by measuring the resonance fluorescence of the qubit, which provides information on both the engineered environment and the coupling between qubit and transmission line. The spectral function of a transmission line without partial reflectors is found to be Ohmic over a wide frequency range, whereas a peaked spectral density is found for the shaped environment. Our work lays the ground for future quantum simulations of other, more involved, impurity models with superconducting circuits.