Chih-Sung Chuu

Memory-built-in quantum teleportation with photonic and atomic qubits

The combination of quantum teleportation1 and quantum memory2,3,4,5 of photonic qubits is essential for future implementations of large-scale quantum communication6 and measurement-based quantum computation7,8. Both steps have been achieved separately in many proof-of-principle experiments9,10,11,12,13,14, but the demonstration of memory-built-in teleportation of photonic qubits remains an experimental challenge. Here, we demonstrate teleportation between photonic (flying) and atomic (stationary) qubits. In our experiment, an unknown polarization state of a single photon is teleported over 7 m onto a remote atomic qubit that also serves as a quantum memory. The teleported state can be stored and successfully read out for up to 8 μs. Besides being of fundamental interest, teleportation between photonic and atomic qubits with the direct inclusion of a readable quantum memory represents a step towards an efficient and scalable quantum network2,3,4,5,6,7,8.

A millisecond quantum memory for scalable quantum networks

calculation shows that the expected lifetime is of the order of seconds in this case. Here we report on our investigation of prolonging the storage time of the quantum memory for single excitations. In the experiment, we find that using only the ‘clock state’ is not sufficient toobtain theexpected longstorage time.We furtheranalyse, isolate and identify the distinct decoherence mechanisms, and thoroughly investigate the dephasing of the spin wave (SW) by varying its wavelength. We find that the dephasing of the SW is extremely sensitive to the angle between the write beam and detection mode, especiallyforsmallangles.Onthebasisofthisfinding,byexploiting the ‘clock state’ and increasing the wavelength of the SW to suppress the dephasing, we succeed in extending the storage time from 10s

Bose Einstein Condensate in a Box

Bose-Einstein condensates have been produced in an optical box trap. This optical trap type has strong confinement in two directions comparable to that which is possible in an optical lattice, yet produces individual condensates rather than the thousands typical of a lattice. The box trap is integrated with single-atom detection capability, paving the way for studies of quantum atom statistics.

Direct Observation of Sub-Poissonian Number Statistics in a Degenerate Bose Gas

We report the direct observation of sub-Poissonian number fluctuation for a degenerate Bose gas confined in an optical trap. Reduction of number fluctuations below the Poissonian limit is observed for average numbers that range from 300 to 60 atoms.

A high frequency optical trap for atoms using Hermite-Gaussian beams

We present an experimental method to create a single high frequency optical trap for atoms based on an elongated Hermite-Gaussian TEM01 mode beam. This trap results in confinement strength similar to that which may be obtained in an optical lattice. We discuss an optical setup to produce the trapping beam and then detail a method to load a Bose-Einstein Condensate (BEC) into a TEM01 trap. Using this method, we have succeeded in producing individual highly confined lower dimensional condensates.

A miniature ultrabright source of temporally long, narrowband biphotons

We demonstrate a miniature source of long biphotons utilizing the cluster effect and double-pass pumping in a monolithic doubly resonant parametric down-converter. We obtain a biphoton correlation time of 17.1 ns with a generation rate of 1.10×105 biphotons/(s mW) and an estimated linewidth of 8.3 MHz.

Hiding Single Photons with Spread Spectrum Technology

We describe a proof-of-principal experiment demonstrating the use of spread spectrum technology at the single photon level. We show how single photons with a prescribed temporal shape, in the presence of interfering noise, may be hidden and recovered.

Ultrabright Backward-wave Biphoton Source

We calculate the propoerties of a novel biphoton source based on resonant backward wave spontaneous parametric down-conversion. We show that the biphotons are generated in a single longitudinal mode having a subnatural linewidth and a correlation time exceeding 65 ns.

Quantum Memory with Optically Trapped Atoms

We report the experimental demonstration of quantum memory for collective atomic states in a far-detuned optical dipole trap. Generation of the collective atomic state is heralded by the detection of a Raman scattered photon and accompanied by storage in the ensemble of atoms. The optical dipole trap provides confinement for the atoms during the quantum storage while retaining the atomic coherence. We probe the quantum storage by cross correlation of the photon pair arising from the Raman scattering and the retrieval of the atomic state stored in the memory. Nonclassical correlations are observed for storage times up to 60 mus.

Modulation and Measurement of Time-Energy Entangled Photons

We describe a proof-of-principle experiment demonstrating a Fourier technique for measuring the shape of biphoton wavepackets that vary rapidly as compared to the speed of available photon detectors. The technique uses synchronously driven telecommunication modulators.