Advances in quantum control of three-level superconducting circuit architectures

  1. G. Falci,
  2. P. G. Di Stefano,
  3. A. Ridolfo,
  4. A. D'Arrigo,
  5. G. S. Paraoanu,
  6. and E. Paladino
Advanced control in Lambda (Λ) scheme of a solid state architecture of artificial atoms and quantized modes would allow the translation to the solid-state realm of a whole class of
phenomena from quantum optics, thus exploiting new physics emerging in larger integrated quantum networks and for stronger couplings. However control solid-state devices has constraints coming from selection rules, due to symmetries which on the other hand yield protection from decoherence, and from design issues, for instance that coupling to microwave cavities is not directly switchable. We present two new schemes for the Λ-STIRAP control problem with the constraint of one or two classical driving fields being always-on. We show how these protocols are converted to apply to circuit-QED architectures. We finally illustrate an application to coherent spectroscopy of the so called ultrastrong atom-cavity coupling regime.

Non-equilibrium thermodynamics of continuously measured quantum systems: a circuit-QED implementation

  1. P. G. Di Stefano,
  2. J. J. Alonso,
  3. E. Lutz,
  4. G. Falci,
  5. and M. Paternostro
We propose a fully operational framework to study the non-equilibrium thermodynamics of a quantum system S that is coupled to a detector D whose state is continuously monitored, allowing
to single out individual quantum trajectories of S. We focus on detailed fluctuation theorems and characterize the entropy production of the system. We establish fundamental differences with respect to the thermodynamic of unmonitored, unitarily evolved systems. We consider the paradigmatic example of circuit-QED, where superconducting qubits can be coupled to a continuously monitored resonator and show numerical simulations using state of the art experimental parameters.

Coherent manipulation of noise-protected superconducting artificial atoms in the Lambda scheme

  1. P. G. Di Stefano,
  2. E. Pladino,
  3. T. J. Pope,
  4. and G. Falci
We propose a new protocol for thr manipulation of a three-level artificial atom in Lambda (Λ) configuration in the absence of a direct pump coupling. It allows faithful, selective
and robust population transfer analogous to stimulated Raman adiabatic passage (Λ-STIRAP), in highly noise protected superconducting artificial atoms. It combines the use of a two-photon pump pulse with suitable advanced control, operated by a slow modulation of the phase of the external fields, leveraging on the stability of semiclassical microwave drives. This protocol is a building block for novel tasks in complex quantum architectures. Its demonstration would be a benchmark for the implementation of a class of multilevel advanced control procedures for quantum computation and microwave quantum photonics in systems based on artificial atoms.

Design of a Lambda system for population transfer in superconducting nanocircuits

  1. G. Falci,
  2. A. La Cognata,
  3. M. Berritta,
  4. A. D'Arrigo,
  5. E. Paladino,
  6. and B. Spagnolo
The implementation of a Lambda scheme in superconducting artificial atoms could allow detec- tion of stimulated Raman adiabatic passage (STIRAP) and other quantum manipulations in the
microwave regime. However symmetries which on one hand protect the system against decoherence, yield selection rules which may cancel coupling to the pump external drive. The tradeoff between efficient coupling and decoherence due to broad-band colored Noise (BBCN), which is often the main source of decoherence is addressed, in the class of nanodevices based on the Cooper pair box (CPB) design. We study transfer efficiency by STIRAP, showing that substantial efficiency is achieved for off-symmetric bias only in the charge-phase regime. We find a number of results uniquely due to non-Markovianity of BBCN, namely: (a) the efficiency for STIRAP depends essentially on noise channels in the trapped subspace; (b) low-frequency fluctuations can be analyzed and represented as fictitious correlated fluctuations of the detunings of the external drives; (c) a simple figure of merit for design and operating prescriptions allowing the observation of STIRAP is proposed. The emerging physical picture also applies to other classes of coherent nanodevices subject to BBCN.

1/f noise: implications for solid-state quantum information

  1. E. Paladino,
  2. Y. M. Galperin,
  3. G. Falci,
  4. and B. L. Altshuler
The efficiency of the future devices for quantum information processing will be limited mostly by the finite decoherence rates of the individual qubits and quantum gates. Recently,
substantial progress was achieved in enhancing the time within which a solid-state qubit demonstrates coherent dynamics. This progress is based mostly on a successful isolation of the qubits from external decoherence sources obtained by clever engineering. Under these conditions, the material-inherent sources of noise start to play a crucial role. In most cases, quantum devices are affected by noise decreasing with frequency f approximately as 1/f. According to the present point of view, such noise is due to material- and device-specific microscopic degrees of freedom interacting with quantum variables of the nanodevice. The simplest picture is that the environment that destroys the phase coherence of the device can be thought of as a system of two-state fluctuators, which experience random hops between their states. If the hopping times are distributed in a exponentially broad domain, the resulting fluctuations have a spectrum close to 1/f in a large frequency range. In this paper we review the current state of the theory of decoherence due to degrees of freedom producing 1/f noise. We discuss basic mechanisms of such noises in various nanodevices and then review several models describing the interaction of the noise sources with quantum devices. The main focus of the review is to analyze how the 1/f noise destroys their coherent operation. We start from individual qubits concentrating mostly on the devices based on superconductor circuits, and then discuss some special issues related to more complicated architectures. Finally, we consider several strategies for minimizing the noise-induced decoherence.