The time-bin quantum state is known to be highly robust against decoherence effects in both fiber-optic and atmospheric channels, a unique feature that renders the time degree of freedom (DOF) more appropriate for quantum communication in these channels. In this paper, we present a scheme to deliver with high fidelity an arbitrary, unknown quantum state in polarization or spatial DOFs over a stochastic channel without need for compensation. The sender swaps the polarization or spatial quantum state for a time-bin state of the photon before signaling it over the random channel, and the receiver swaps the state back. Because the signaled photon is assumed to be in a single spatial or polarization mode, no modal-dependent channel effects perturb the time-bin state. We find that by migration to the time bin, the fidelity of the transferred state is boosted by a margin dependent on the time-bin period and the standard deviations of the statistical parameters of the channel.
The time-bin quantum state is known to be highly robust against decoherence effects in both fiber-optic and atmospheric channels, a unique feature that renders the time degree of freedom (DOF) more appropriate for quantum communication in these channels. In this paper, we present a scheme to deliver with high fidelity an arbitrary, unknown quantum state in polarization or spatial DOFs over a stochastic channel without need for compensation. The sender swaps the polarization or spatial quantum state for a time-bin state of the photon before signaling it over the random channel, and the receiver swaps the state back. Because the signaled photon is assumed to be in a single spatial or polarization mode, no modal-dependent channel effects perturb the time-bin state. We find that by migration to the time bin, the fidelity of the transferred state is boosted by a margin dependent on the time-bin period and the standard deviations of the statistical parameters of the channel.
This work deals with creation, manipulation and detection of quantum photon states, in one and two degrees of freedom, encoded in polarization and time-bin basis. A particular quantum state, an entangled state, carries a wide range of implementations, that are impossible via classical tasks, such as teleportation, dense coding, and quantum communication protocols. One of these tasks, quantum cryptography, allows intrinsically secure transmission of information. Nowadays, quantum key distribution is implemented in intercity quantum networks, by using telecommunication fibers to connect nodes within the network. In future scenarios, photons could travel through greater distances, but, due to losses, fiber links need for quantum repeater, a very demanding engineering solution. An alternative way, is the use of free-space satellite quantum networks. Here we focus on polarization and time bin degrees of freedom (DOFs) of the photons as a resource for quantum information. In particular we study the possibility to share an hyper-entangled state in polarization and time-bin DOFs between two spatially separated users. In addition we study a new tomographic method, based on compressed sensing, to recover the density matrix of a quantum state when prior information are available. Typical implementation of time-bin photon source, based on Franson’s scheme, suffers on intrinsic loophole. To overcome that we experimentally demonstrated that with a time-bin source it is possible to obtain a very high visibility in order to violate a chained Bell inequality. Interference at single photon level through satellite-ground channels is presented here, showing that, temporal encoding is preserved along turbulent channels. With this experiment we show that temporal encoding can be use for a future implementation of satellite quantum communication. Finally, to complete this work, we demonstrate a new method to certified the randomness of a source, useful in many task, such as quantum cryptography by using a polarization entangled photons source.
Encoding quantum information in photonic time-bin states is typically considered impractical for moving free-space quantum communication due to the difficulties with phase stabilization of distant quantum time-bin interferometers and turbulence of free-space channels. We demonstrate a novel approach using reference frame independent time-bin quantum key distribution that completely avoids the need for active relative phase stabilization while simultaneously overcoming a highly multi-mode channel without any active mode filtering. This scheme enables passive, self-compensating time-bin quantum communication without any mode filtering, mode sorting, adaptive optics, active basis selection, or active phase alignment. We realize a proof-of-concept demonstration using hybrid polarization and time-bin entangled photons that demonstrates a sustained asymptotic secure key rate greater than 0.07 bits/coincidence over a 15 m multi-mode fiber optical channel and showing entanglement correlations over a moving 38.5 dB loss free-space channel, including system losses. The scheme simplifies the use of time-bin encoding and can be readily applied over various spatially multi-mode and fluctuating channels involving rapidly moving platforms, including airborne and satellite systems.
Abstract In quantum communication, the channel noise and the misalignment of the reference frames between the communication parties will lead to the failure of quantum state transmission. Here an alignment‐free spatial‐polarization hyperentanglement transmission scheme is provided for hyperentangled photons. In this scheme, before the spatial‐polarization hyperentanglement is transmitted through the fiber channel, it is first encoded as a time‐bin entanglement with the same polarization. After the photons pass through the noise channel, the polarization errors caused by reference frames misalignment and channel noise can be corrected by time‐bin entanglement. In principle, by implementing this scheme, the communication parties can share the original hyperentangled state, and the success probability can approach unity. The scheme is robust to random channel noise and reference frames misalignment, and the decoherence effect caused by the misalignment of the reference frames between the communication parties can be completely suppressed by implementing this scheme.
Despite its widespread use in fiber optics, encoding quantum information in photonic time-bin states is usually considered impractical for free-space quantum communication as turbulence-induced spatial distortion impedes the analysis of time-bin states at the receiver. Here, we demonstrate quantum key distribution using time-bin photonic states distorted by turbulence and depolarization during free-space transmission. Utilizing a novel analyzer apparatus, we observe stable quantum bit error ratios of 5.32 %, suitable for generating secure keys, despite significant wavefront distortions and polarization fluctuations across a 1.2 km channel. This shows the viability of time-bin quantum communication over long-distance free-space channels, which will simplify direct fiber/free-space interfaces and enable new approaches for practical free-space quantum communication over multi-mode, turbulent, or depolarizing channels.
Faithful transmission of quantum information over noisy channel is an essential requisite for quantum communication and distributed quantum computing. Here we experimentally demonstrate a noise-rejecting scheme for single-photon qubits transmission, resorting to neither ancillary photons nor globally entangled resources. Employing the unbalanced polarization interferometer, the polarization qubits are transformed to time-bin degrees of freedom. Meanwhile, the deterministic transmission of quantum states with high fidelity can be achieved. We find that the immunity of time-bin encoded qubits against collective noise paves the way to practical quantum error-correction and rejection in long-distance quantum communication.
Multi-degree-of-freedom photonic quantum processing requires routing between degree-of-freedom (DOF) qubit encodings on a single photon. A SWAP between polarization and time-bin qubits is an advantageous primitive for such architectures, however conventional early/late time-bin encoding does not support bidirectional logical time-bin flips from late to early which limits the ability to implement certain quantum operations. We introduce a parity-based time-bin encoding in which logical ∣0⟩T and ∣1⟩T correspond to even and odd multiples of a spacing Δt, so that a physical delay of Δt implements ∣0⟩T↔∣1⟩T. This encoding is the enabling ingredient that makes a polarization-controlled delay line implement CNOTP→T and aligns naturally with periodic refractive index modulation for CNOTT→P. Composing three such CNOT operations sequentially results in a deterministic SWAP between polarization and time-bin degrees of freedom. We quantify how EOM voltage errors reduce the polarization-flip probability and estimate timing requirements from modulator switching, detector resolution, and timing jitter, giving an illustrative timing budget.