Quantum Communication with Time-Bin Encoded Microwave Photons

Abstract

Heralding techniques are useful in quantum communication to circumvent losses without resorting to error correction schemes or quantum repeaters. Such techniques are realized, for example, by monitoring for photon loss at the receiving end of the quantum link while not disturbing the transmitted quantum state. We describe and experimentally benchmark a scheme that incorporates error detection in a quantum channel connecting two transmon qubits using traveling microwave photons. This is achieved by encoding the quantum information as a time-bin superposition of a single photon, which simultaneously realizes high communication rates and high fidelities. The presented scheme is straightforward to implement in circuit QED and is fully microwave-controlled, making it an interesting candidate for future modular quantum computing architectures.Engineering of large-scale quantum systems will likely require coherent exchange of quantum states between distant units. The concept of quantum networks has been studied theoretically [1][2][3][4] and substantial experimental efforts have been devoted to distribute entanglement over increasingly larger distances [5][6][7][8][9][10][11][12][13][14][15]. In practice, quantum links inevitably experience losses, which vary significantly between different architectures and may range from 2×10 −4 dB/m in optical fibers [16] to 5×10 −3 dB/m in superconducting coaxial cables and waveguides at cryogenic temperatures [17]. However, no matter which architecture is used, the losses over a sufficiently long link will eventually destroy the coherence of the transmitted quantum state, unless some measures are taken to mitigate these losses. Possible ways to protect the transmitted quantum information rely, for example, on using quantum repeaters [18,19], error correcting schemes [20][21][22] or heralding protocols [23][24][25][26], which allow one to retransmit the information in case photon loss is detected.Heralding protocols are particularly appealing for near-term scaling of quantum systems since they are implementable without a significant resource overhead and can provide deterministic remote entanglement at predetermined times [27]. In essence, these protocols rely on encoding the transmitted quantum information in a suitably chosen subspace S such that any error, which may be encountered during transmission, causes the system to leave this subspace. On the receiving end, a measurement which determines whether the system is in S but does not distinguish between individual states within S, can be used to detect if an error occurred. Crucially, when the transfer is successful, this protocol does not disturb the transmitted quantum information. As a counter * P.K. and M.P. contributed equally to this work.philipp.kurpiers@phys.ethz.ch, mpechal@stanford.edu, andreas.wallraff@phys.ethz.ch example, a simple encoding as a superposition of the vacuum state |0 and the single photon Fock state |1 is not suitable to detect errors due to photon loss because the error does not cause a transition out ...

Realizing a deterministic source of multipartite-entangled photonic qubits

“…As interesting future directions, one could explore applications of the presented source for one-way quantum computing with cluster states 6 , 26 , 27 , Heisenberg-limited metrology, or teleportation with GHZ states 28 – 30 , or photon loss resilient quantum communication with W states 31 , 32 . In addition, this versatile source of quantum many-body states of electromagnetic radiation, able to perform generic gates of the CNOT and SWAP families, could be used to access a larger variety of quantum many-body states in the MPS family, e.g., as ground states of variational quantum algorithms 33 , 34 .…”

Rapid and Unconditional Parametric Reset Protocol for Tunable Superconducting Qubits

“…Beyond qubit reset, parametric modulation-induced interaction can also be used in thermodynamic reservoir engineering [38,49] and quantum many-body simulations [50]. Furthermore, this work provides an efficient way to entangle the qubit state with an itinerant single photon, particularly useful in quantum communication and quantum network application [51][52][53].…”

Non-destructive optical readout of a superconducting qubit

“…However, transducing quantum signals between these disparate regimes of the electromagnetic spectrum remains an outstanding goal [2][3][4][5][6][7], and interfacing superconducting qubits with electro-optic transducers presents significant challenges due to the deleterious effects of optical photons on superconductors [8,9]. Moreover, many remote entanglement protocols [10][11][12][13] require multiple qubit gates both preceding and following the upconversion of the quantum state, and thus an ideal transducer should leave the state of the qubit unchanged: more precisely, the backaction [14] from the transducer on the qubit should be minimal. Here we demonstrate non-destructive optical readout of a superconducting transmon qubit via a continuously operated electro-optic transducer.…”