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1.
Science ; 385(6705): 179-183, 2024 Jul 12.
Article in English | MEDLINE | ID: mdl-38991069

ABSTRACT

Quantum computation and quantum communication are expected to provide users with capabilities inaccessible by classical physics. However, scalability to larger systems with many qubits is challenging. One solution is to develop a quantum network consisting of small-scale quantum registers containing computation qubits that are reversibly interfaced to communication qubits. In this study, we report on a register that uses both optical tweezers and optical lattices to deterministically assemble a two-dimensional array of atoms in an optical cavity. Harnessing a single atom-addressing beam, we stimulate the emission of a photon from each atom and demonstrate multiplexed atom-photon entanglement with a generation-to-detection efficiency approaching 90%. Combined with cavity-mediated quantum logic, our approach provides a possible route to distributed quantum information processing.

2.
Phys Rev Lett ; 126(25): 253603, 2021 Jun 25.
Article in English | MEDLINE | ID: mdl-34241514

ABSTRACT

Nondestructive quantum measurements are central for quantum physics applications ranging from quantum sensing to quantum computing and quantum communication. Employing the toolbox of cavity quantum electrodynamics, we here concatenate two identical nondestructive photon detectors to repeatedly detect and track a single photon propagating through a 60 m long optical fiber. By demonstrating that the combined signal-to-noise ratio of the two detectors surpasses each single one by about 2 orders of magnitude, we experimentally verify a key practical benefit of cascaded nondemolition detectors compared to conventional absorbing devices.

3.
Phys Rev Lett ; 126(13): 130502, 2021 Apr 02.
Article in English | MEDLINE | ID: mdl-33861090

ABSTRACT

Quantum teleportation enables the deterministic exchange of qubits via lossy channels. While it is commonly believed that unconditional teleportation requires a preshared entangled qubit pair, here we demonstrate a protocol that is in principle unconditional and requires only a single photon as an ex-ante prepared resource. The photon successively interacts, first, with the receiver and then with the sender qubit memory. Its detection, followed by classical communication, heralds a successful teleportation. We teleport six mutually unbiased qubit states with average fidelity F[over ¯]=(88.3±1.3)% at a rate of 6 Hz over 60 m.

4.
Science ; 371(6529): 614-617, 2021 02 05.
Article in English | MEDLINE | ID: mdl-33542133

ABSTRACT

The big challenge in quantum computing is to realize scalable multi-qubit systems with cross-talk-free addressability and efficient coupling of arbitrarily selected qubits. Quantum networks promise a solution by integrating smaller qubit modules to a larger computing cluster. Such a distributed architecture, however, requires the capability to execute quantum-logic gates between distant qubits. Here we experimentally realize such a gate over a distance of 60 meters. We employ an ancillary photon that we successively reflect from two remote qubit modules, followed by a heralding photon detection, which triggers a final qubit rotation. We use the gate for remote entanglement creation of all four Bell states. Our nonlocal quantum-logic gate could be extended both to multiple qubits and many modules for a tailor-made multi-qubit computing register.

5.
Phys Rev Lett ; 123(3): 030501, 2019 Jul 19.
Article in English | MEDLINE | ID: mdl-31386433

ABSTRACT

The generation and distribution of entanglement are key resources in quantum repeater schemes. Temporally multiplexed systems offer time-bin encoding of quantum information which provides robustness against decoherence in fibers, crucial in long distance communication. Here, we demonstrate the direct generation of entanglement in time between a photon and a collective spin excitation in a rare earth ion doped ensemble. We analyze the entanglement by mapping the atomic excitation onto a photonic qubit and by using time-bin qubit analyzers implemented with another doped crystal using the atomic frequency comb technique. Our results provide a solid-state source of entangled photons with embedded quantum memory. Moreover, the quality of the entanglement is high enough to enable a violation of a Bell inequality by more than two standard deviations.

6.
Nat Commun ; 8: 14072, 2017 01 19.
Article in English | MEDLINE | ID: mdl-28102203

ABSTRACT

Strong interaction between two single photons is a long standing and important goal in quantum photonics. This would enable a new regime of nonlinear optics and unlock several applications in quantum information science, including photonic quantum gates and deterministic Bell-state measurements. In the context of quantum networks, it would be important to achieve interactions between single photons from independent photon pairs storable in quantum memories. So far, most experiments showing nonlinearities at the single-photon level have used weak classical input light. Here we demonstrate the storage and retrieval of a paired single photon emitted by an ensemble quantum memory in a strongly nonlinear medium based on highly excited Rydberg atoms. We show that nonclassical correlations between the two photons persist after retrieval from the Rydberg ensemble. Our result is an important step towards deterministic photon-photon interactions, and may enable deterministic Bell-state measurements with multimode quantum memories.

7.
Phys Rev Lett ; 111(3): 033603, 2013 Jul 19.
Article in English | MEDLINE | ID: mdl-23909318

ABSTRACT

Interference of light fields plays an important role in various high-precision measurement schemes. It has been shown that superresolving phase measurements beyond the standard coherent state limit can be obtained either by using maximally entangled multiparticle states of light or using complex detection approaches. Here we show that superresolving phase measurements at the shot noise limit can be achieved without resorting to nonclassical optical states or to low-efficiency detection processes. Using robust coherent states of light, high-efficiency homodyne detection, and a deterministic binarization processing technique, we show a narrowing of the interference fringes that scales with 1/√[N] where N is the mean number of photons of the coherent state. Experimentally we demonstrate a 12-fold narrowing at the shot noise limit.

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