Quantum process tomography of a high-dimensional quantum communication channel

Abstract

The characterization of quantum processes, e.g. communication channels, is an essential ingredient for establishing quantum information systems. For quantum key distribution protocols, the amount of overall noise in the channel determines the rate at which secret bits are distributed between authorized partners.In particular, tomographic protocols allow for the full reconstruction, and thus characterization, of the channel. Here, we perform quantum process tomography of high-dimensional quantum communication channels with dimensions ranging from 2 to 5. We can thus explicitly demonstrate the effect of an eavesdropper performing an optimal cloning attack or an interceptresend attack during a quantum cryptographic protocol. Moreover, our study shows that quantum process tomography enables a more detailed understanding of the channel conditions compared to a coarse-grained measure, such as quantum bit error rates. This full characterization technique allows us to optimize the performance of quantum key distribution under asymmetric experimental conditions, which is particularly useful when considering high-dimensional encoding schemes.

High-dimensional quantum gates using full-field spatial modes of photons

“…1b. Since simple cross-talk matrices cannot directly reveal information about the unitarity of the mode transformation, we also perform a full high-dimensional quantum process tomography [55] on the simulated 3-dimensional X 1 -gate. Quantum process tomography is based on a set of informationally complete measurements for a given set of input states, leading to a complete characterisation of the corresponding quantum channel.…”

“…In addition, we implement also combinedXĤ-gates in dimension three, in particular aX 1Ĥ 2-gate shown in (c) and aX 1Ĥ † 1gate shown in (d). Note that measuring p-modes properly in different mutually unbiased bases has only become possible recently [55]. configuration of the multiport, i.e.…”

Classical Shadows for Quantum Process Tomography on Near-term Quantum Computers

“…Earlier attempts at QPT used the linear inversion method [7,8]. Later various statistical methods were developed including maximum likelihood methods [9][10][11][12][13], Bayesian methods [14][15][16], compressed sensing methods [17], tensor network methods [18] and other optimization techniques [19][20][21][22][23][24][25]. Theoretically, quantum process tomography can be related to quantum state tomography through the Jamio lkowski process-state isomorphism [26,27].…”

Proof-of-principle experimental demonstration of quantum gate verification

“…To make good use of quantum information technology, it is first necessary to characterize quantum devices to evaluate their performance. The standard method for characterizing quantum devices is quantum process tomography (QPT) [1][2][3][4][5][6][7], which allows complete reconstruction of the quantum process of the device, but its resource overhead grows exponentially with the size of the system, making it impractical when the system is large. However, for most applications, the complete information of the quantum device is not needed, but only the fidelity of the evaluated device compared to a perfect device.…”