Selective and Efficient Quantum Process Tomography without Ancilla

Abstract

Several methods, known as quantum process tomography, are available to characterize the evolution of quantum systems, a task of crucial importance. However, their complexity dramatically increases with the size of the system. Here we present a new method for quantum process tomography. We describe a new algorithm that can be used to selectively estimate any parameter characterizing a quantum process. Unlike any of its predecessors this new quantum tomographer combines two virtues: it requires investing a number of physical resources scaling polynomially with the number of qubits and at the same time it does not require any ancillary resources. We present the results of the first implementation of this quantum device, characterizing quantum processes affecting two qubits encoded in heralded single photons. Even for this small system our method displays clear advantages over the other existing ones.

The two-qubit amplitude damping channel: Characterization using quantum stabilizer codes

“…Other techniques includes characterization of the noise using an efficient method for transforming a quantum channel or process into a symmetric channel having only diagonal elements in the process matrix via twirling [23,24]. A method similar to [23], but extended to estimate any given off-diagonal term, was introduced in [25] and it was further extended to perform process tomography with out using any ancilla in [26].…”

Process estimation in the presence of time-invariant memory effects

“…It is known to be a complex task, however, under certain assumptions it can be efficiently applied also to large systems [6][7][8][9][10][11] and even the accuracy can be assessed [12][13][14][15]. QPT deals with a scenario when an experimenter is given an unknown input-output black box E. In each run of the experiment he prepares some test state ̺ and performs a measurement M , thus, he choses the setting x = (̺, M ), and, records the outcome E k , where E k ∈ M .…”

Property testing of unitary operators

“…Even if this operation is known to be unitary, it still needs Θ(4 n ) observables. Although many improvements and variants of QPT have been proposed [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], in general the resource consumption of this approach still grows quickly as the system becomes large.…”