Andrew MacRae

Quantum-optical state engineering up to the two-photon level

Tailoring of arbitrary single-mode states of travelling light up to the two-photon level is proposed and demonstrated. The desired state is remotely prepared in the signal channel of spontaneous parametric down-conversion by means of conditional measurements on the idler channel.

Versatile Wideband Balanced Detector for Quantum Optical Homodyne Tomography

We present a comprehensive theory and an easy to follow method for the design and construction of a wideband homodyne detector for time-domain quantum measurements. We show how one can evaluate the performance of a detector in a specific time-domain experiment based on the electronic spectral characteristic of that detector. We then present and characterize a high-performance detector constructed using inexpensive, commercially available components such as low-noise high-speed operational amplifiers and high-bandwidth photodiodes. Our detector shows linear behavior up to a level of over 13 dB clearance between shot noise and electronic noise, in the range from DC to 100 MHz. The detector can be used for measuring quantum optical field quadratures both in the continuous-wave and pulsed regimes with standard commercial mode-locked lasers.

A versatile digital GHz phase lock for external cavity diode lasers

We present a versatile, inexpensive and simple optical phase lock for applications in atomic physics experiments. Thanks to all-digital phase detection and implementation of beat frequency pre-scaling, the apparatus requires no microwave-range reference input, and permits phase locking at frequency differences ranging from sub-MHz to 7 GHz (and with minor extension, to 12 GHz). The locking range thus covers ground state hyperfine splittings of all alkali metals, which makes this system a universal tool for many experiments on coherent interaction between light and atoms.

Tomography of a high-purity narrowband photon from a transient atomic collective excitation.

We demonstrate efficient heralded generation of high purity narrow-bandwidth single photons from a transient collective spin excitation in a hot atomic vapor cell. Employing optical homodyne tomography, we fully reconstruct the density matrix of the generated photon and observe a Wigner function reaching the zero value without correcting for any inefficiencies. The narrow bandwidth of the photon produced is accompanied by a high generation rate yielding a high spectral brightness. The source is, therefore, compatible with atomic-based quantum memories as well as other applications in light-atom interfacing. This Letter paves the way to preparing and measuring arbitrary superposition states of collective atomic excitations.

Matched slow pulses using double electromagnetically induced transparency

We implement double electromagnetically induced transparency (DEIT) in rubidium vapor using a tripod-shaped energy-level scheme consisting of hyperfine magnetic sublevels of the 5S1/2-->5P1/2 transition. We show experimentally that through the use of DEIT one can control the contrast of transparency windows as well as group velocities of the two signal fields. In particular, the group velocities can be equalized, which holds promise to greatly enhance nonlinear optical interaction between these fields.

Complete temporal characterization of a single photon

A convenient scheme for characterizing the temporal properties of a single photon looks set to aid experiments in quantum optics. An international team of scientists from Canada, China, USA, Uruguay and Russia says that this approach can be used to determine the complete mode structure of a photon, in particular, the real and imaginary parts of its temporal density matrix. This information is important for quantum communication experiments for which it is often critical to match photon modes. The characterization scheme, which the researchers term polychromatic optical heterodyne tomography, works by collecting autocorrelation data of homodyne photocurrent at multiple local oscillator frequencies. The team says that tests of the technique with single photons generated by four-wave mixing in an atomic vapour agree well with theoretical predictions.

Generation and tomography of arbitrary optical qubits using transient collective atomic excitations

We demonstrate the preparation of heralded Fock-basis qubits (a|0〉+b|1〉) from transient collective spin excitations in a hot atomic vapor. The preparation event is heralded by Raman-scattered photons in a four-wave mixing process seeded by a weak coherent optical excitation. The amplitude and phase of the seed field allow arbitrary control over the qubit coefficients. The qubit state is characterized using balanced homodyne tomography.

Narrowband Photon From an Atomic Source

We demonstrate efficient generation of narrow-bandwidth photon superposition states. Since the heralded states stem from a transient collective spin excitation in the atomic ensemble, this work allows the engineering of arbitrary collective atomic excitation states.

Simultaneous Slow Light Pulses With Matched Group Velocities via Double‐EIT

We demonstrate double electromagnetically induced transparency in rubidium vapor, in which two weak signal fields are simultaneously slowed or stored when a single pump field is applied. By manipulating the relative field strengths, we are able to control the group velocity of the pulses. In order to explore these effects, we develop a theoretical model of the atomic system used in the experiment.