arXiv subjects

M. Mohseni

Publications and source records attributed to M. Mohseni.

28 records · Page 2Linked to original sources

arXiv2009

Equation of motion for process matrix: Hamiltonian identification and dynamical control of open quantum systems

We develop a general approach for monitoring and controlling evolution of open quantum systems. In contrast to the master equations describing time evolution of density operators, here, we formulate a dynamical equation for the evolution of the process matrix acting on a system. This equation is applicable to non-Markovian and/or strong coupling regimes. We propose two distinct applications for this dynamical equation. We first demonstrate identification of quantum Hamiltonians generating dynamics of closed or open systems via performing process tomography. In particular, we argue how one can efficiently estimate certain classes of sparse Hamiltonians by performing partial tomography schemes. In addition, we introduce a novel optimal control theoretic setting for manipulating quantum dynamics of Hamiltonian systems, specifically for the task of decoherence suppression.

quant-ph↗

arXiv2009

Quantum Process Estimation via Generic Two-Body Correlations

Performance of quantum process estimation is naturally limited to fundamental, random, and systematic imperfections in preparations and measurements. These imperfections may lead to considerable errors in the process reconstruction due to the fact that standard data analysis techniques presume ideal devices. Here, by utilizing generic auxiliary quantum or classical correlations, we provide a framework for estimation of quantum dynamics via a single measurement apparatus. By construction, this approach can be applied to quantum tomography schemes with calibrated faulty state generators and analyzers. Specifically, we present a generalization of "Direct Characterization of Quantum Dynamics" [M. Mohseni and D. A. Lidar, Phys. Rev. Lett. 97, 170501 (2006)] with an imperfect Bell-state analyzer. We demonstrate that, for several physically relevant noisy preparations and measurements, only classical correlations and small data processing overhead are sufficient to accomplish the full system identification. Furthermore, we provide the optimal input states for which the error amplification due to inversion on the measurement data is minimal.

quant-ph↗

arXiv2008

Direct Estimation of Single- and Two-Qubit Hamiltonians and Relaxation Rates

We provide a novel approach for characterization of quantum Hamiltonian systems via utilizing a single measurement device. Specifically, we demonstrate how external quantum correlations can be used for Hamiltonian identification tasks. We explicitly introduce experimental procedures for direct estimation of single- and two-qubit Hamiltonian parameters, and also for simultaneous estimation of transverse and longitudinal relaxation rates, using a single Bell-state analyzer. An advantage of our method over the earlier approaches is that it has a built-in feature which makes it suitable for partial characterization of Hamiltonian parameters.

quant-ph↗

arXiv2008

Quantum Process Tomography: Resource Analysis of Different Strategies

Characterization of quantum dynamics is a fundamental problem in quantum physics and quantum information science. Several methods are known which achieve this goal, namely Standard Quantum Process Tomography (SQPT), Ancilla-Assisted Process Tomography (AAPT), and the recently proposed scheme of Direct Characterization of Quantum Dynamics (DCQD). Here, we review these schemes and analyze them with respect to some of the physical resources they require. Although a reliable figure-of-merit for process characterization is not yet available, our analysis can provide a benchmark which is necessary for choosing the scheme that is the most appropriate in a given situation, with given resources. As a result, we conclude that for quantum systems where two-body interactions are not naturally available, SQPT is the most efficient scheme. However, for quantum systems with controllable two-body interactions, the DCQD scheme is more efficient than other known QPT schemes in terms of the total number of required elementary quantum operations.

quant-ph↗

arXiv2007

Direct Characterization of Quantum Dynamics: General Theory

The characterization of the dynamics of quantum systems is a task of both fundamental and practical importance. A general class of methods which have been developed in quantum information theory to accomplish this task is known as quantum process tomography (QPT). In an earlier paper [M. Mohseni and D. A. Lidar, Phys. Rev. Lett. 97, 170501 (2006)] we presented a new algorithm for Direct Characterization of Quantum Dynamics (DCQD) of two-level quantum systems. Here we provide a generalization by developing a theory for direct and complete characterization of the dynamics of arbitrary quantum systems. In contrast to other QPT schemes, DCQD relies on quantum error-detection techniques and does not require any quantum state tomography. We demonstrate that for the full characterization of the dynamics of n d-level quantum systems (with d a power of a prime), the minimal number of required experimental configurations is reduced quadratically from d^{4n} in separable QPT schemes to d^{2n} in DCQD.

quant-ph↗

arXiv2007

Direct Characterization of Quantum Dynamics

The characterization of quantum dynamics is a fundamental and central task in quantum mechanics. This task is typically addressed by quantum process tomography (QPT). Here we present an alternative "direct characterization of quantum dynamics" (DCQD) algorithm. In contrast to all known QPT methods, this algorithm relies on error-detection techniques and does not require any quantum state tomography. We illustrate that, by construction, the DCQD algorithm can be applied to the task of obtaining partial information about quantum dynamics. Furthermore, we argue that the DCQD algorithm is experimentally implementable in a variety of prominent quantum information processing systems, and show how it can be realized in photonic systems with present day technology.

quant-ph↗

arXiv2006

Reply to M. Ziman's "Notes on optimality of direct characterization of quantum dynamics"

Recently M. Ziman [quant-ph/0603151] criticized our approach for quantifying the required physical resources in the theory of Direct Characterization of Quantum Dynamics (DCQD) [quant-ph/0601033, quant-ph/0601034] in comparison to other quantum process tomography (QPT) schemes. Here we argue that Ziman's comments regarding optimality, quantumness, and the novelty of DCQD are inaccurate. Specifically, we demonstrate that DCQD is optimal with respect to both the required number of experimental configurations and the number of possible outcomes over all known QPT schemes in the 2^{2n} dimensional Hilbert space of n system and n ancilla qubits. Moreover, we show DCQD is more efficient than all known QPT schemes in the sense of overall required number of quantum operations. Furthermore, we argue that DCQD is a new method for characterizing quantum dynamics and cannot be considered merely as a subclass of previously known QPT schemes.

quant-ph↗

arXiv2005

Worldline deviations of charged spinning particles

The geodesic deviation equation is generalized to worldline deviation equations describing the relative accelerations of charged spinning particles in the framework of Dixon-Souriau equations of motion.

gr-qc↗

arXiv2004

Fault-Tolerant Quantum Computation via Exchange interactions

Quantum computation can be performed by encoding logical qubits into the states of two or more physical qubits, and controlling a single effective exchange interaction and possibly a global magnetic field. This "encoded universality" paradigm offers potential simplifications in quantum computer design since it does away with the need to perform single-qubit rotations. Here we show that encoded universality schemes can be combined with quantum error correction. In particular, we show explicitly how to perform fault-tolerant leakage correction, thus overcoming the main obstacle to fault-tolerant encoded universality.

quant-ph↗

arXiv2000

Gravitational waves and spinning test particles

The motion of a classical spinning test particle in the field of a weak plane gravitational wave is studied. It is found that the characteristic dimensions of the particle's orbit is sensitive to the ratio of the spin to the mass of the particle. The results are compared with the corresponding motion of a particle without spin.

gr-qc↗