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 intercept-resend 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.
Highlights
Quantum information science has witnessed the emergence of a wide range of new technologies and applications [1]
quantum process tomography (QPT) has been performed to characterize several quantum physical systems, such as liquid-state NMR [7, 8], photonic qubits [9], atoms in optical lattices [10], trapped ions [11], solid-state qubits [12], continuous-variable quantum states [13], semiconductor quantum dot qubits [14] and, recently, nonlinear optical systems [15]. Another class of important quantum systems that can benefit from full characterization are quantum channels and components for quantum key distribution (QKD) and quantum communications [16, 17], where, so far, quantum channels may be categorized as optical fibre [18], line-of-sight free-space [19] and groundto-satellite [20] links
Our experiment consists of three components: the generation stage, the quantum channel and the detection stage, which are owned by Alice, Eve and Bob, respectively
Summary
Quantum information science has witnessed the emergence of a wide range of new technologies and applications [1]. QPT has been performed to characterize several quantum physical systems, such as liquid-state NMR [7, 8], photonic qubits [9], atoms in optical lattices [10], trapped ions [11], solid-state qubits [12], continuous-variable quantum states [13], semiconductor quantum dot qubits [14] and, recently, nonlinear optical systems [15] Another class of important quantum systems that can benefit from full characterization are quantum channels and components for quantum key distribution (QKD) and quantum communications [16, 17], where, so far, quantum channels may be categorized as optical fibre [18], line-of-sight free-space [19] and groundto-satellite (satellite-to-ground) [20] links. This full characterization will allow us to complement the numerical approach in [22] to optimize secure key rates under specific experimental conditions and to develop new protocols lacking symmetry that may outperform existing approaches
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