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Transmitting quantum information between two remote parties is a requirement for many quantum applications; however, direct transmission of states is often impossible because of noise and loss in the communication channel. Entanglement-enhanced state communication can be used to avoid this issue, but current techniques require extensive experimental resources to transmit large quantum states deterministically. To reduce these resource requirements, we use photon pairs hyperentangled in polarization and orbital angular momentum to implement superdense teleportation, which can communicate a specific class of single-photon ququarts. We achieve an average fidelity of 87.0(1)%, almost twice the classical limit of 44% with reduced experimental resources than traditional techniques. We conclude by discussing the information content of this constrained set of states and demonstrate that this set has an exponentially larger state space volume than the lower-dimensional general states with the same number of state parameters.

We consider the use of cyclic weak measurements to improve the sensitivity of weak-value amplification precision measurement schemes. Previous weak-value experiments have used only a small fraction of events, while discarding the rest through the process of "post-selection". We extend this idea by considering recycling of events which are typically unused in a weak measurement. Here we treat a sequence of polarized laser pulses effectively trapped inside an interferometer using a Pockels cell and polarization optics. In principle, all photons can be post-selected, which will improve the measurement sensitivity. We first provide a qualitative argument for the expected improvements from recycling photons, followed by the exact result for the recycling of collimated beam pulses, and numerical calculations for diverging beams. We show that beam degradation effects can be mitigated via profile flipping or Zeno reshaping. The main advantage of such a recycling scheme is an effective power increase, while maintaining an amplified deflection.

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We use hyperentangled photons to experimentally implement an entanglement-assisted quantum process tomography technique known as Direct Characterization of Quantum Dynamics. Specifically, hyperentanglement-assisted Bell-state analysis enabled us to characterize a variety of singlequbit quantum processes using far fewer experimental configurations than are required by Standard Quantum Process Tomography (SQPT). Furthermore, we demonstrate how known errors in Bellstate measurement may be compensated for in the data analysis. Using these techniques, we have obtained single-qubit process fidelities as high as 98.2% but with one-third the number experimental configurations required for SQPT. Extensions of these techniques to multi-qubit quantum processes are discussed.PACS numbers: 03.65.WjAs scientists advance the frontiers of quantum information science and quantum computing by producing ever larger and more complex quantum systems, there has been an increased need for efficient methods of characterizing quantum states and processes. The information contained in a quantum system may be extracted by a technique known as Quantum State Tomography (QST), which is accomplished by making various measurements on multiple copies of the state, and then using these measurement outcomes to reconstruct the density matrix. Similarly, the information describing a quantum process is extracted by probing the process with various quantum states and then making measurements on the output. This characterization, known as Quantum Process Tomography (QPT), is generally more difficult than QST because quantum processes contain quadratically more information than the states on which they operate. Because of this difficulty, many different techniques have been invented to characterize quantum processes. We present an experimental realization of a QPT technique devised by Mohseni and Lidar [1], known as Direct Characterization of Quantum Dynamics (DCQD). DCQD has the advantage over other QPT methods in that it both requires far fewer experimental settings than techniques which use only local probe states and measurements, and it requires less complicated-but physically realizablemeasurements than other techniques requiring a similar number of experimental configurations.The biggest challenge in applying DCQD for optical qubits is performing the required full Bell-state analysis (BSA) on each output state, which is impossible using only linear optics and a restricted Hilbert space [2]. DCQD was implemented with photons by Wang et al. using a probabilistic BSA [3]; however, the lack of full BSA meant that substantially more measurements per experimental configuration were required, losing much of the DCQD advantage. However, we have previously shown that it is possible to achieve full BSA using quantum systems that are hyperentangled-simultaneously entangled in multiple degrees of freedom [4]. In fact, DCQD using such deterministic BSA was demonstrated by Liu et al. [5], but was achieved using only single-photon hybridentangled states (entan...

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