No abstract

Kernel methods have a wide spectrum of applications in machine learning. Recently, a link between quantum computing and kernel theory has been formally established, opening up opportunities for quantum techniques to enhance various existing machine-learning methods. We present a distance-based quantum classifier whose kernel is based on the quantum state fidelity between training and test data. The quantum kernel can be tailored systematically with a quantum circuit to raise the kernel to an arbitrary power and to assign arbitrary weights to each training data. Given a specific input state, our protocol calculates the weighted power sum of fidelities of quantum data in quantum parallel via a swap-test circuit followed by two single-qubit measurements, requiring only a constant number of repetitions regardless of the number of data. We also show that our classifier is equivalent to measuring the expectation value of a Helstrom operator, from which the well-known optimal quantum state discrimination can be derived. We demonstrate the performance of our classifier via classical simulations with a realistic noise model and proof-of-principle experiments using the IBM quantum cloud platform.

When four photons arrive at a beam splitter, two from each side, a four-photon, six-path interference effect occurs to yield a sixfold enhancement of the probability for all four photons to exit together from the beam splitter. We produce the four-photon state by using the stimulated emission process in a pulsed parametric down-conversion and measure the probability for all four photons to exit from one side of the beam splitter. The observed enhancement factor is in good agreement with a multimode treatment of pulsed down-conversion. PACS numbers: 42.50.Dv, 03.65.Bz, 42.25.Hz The generation of multiparticle entangled quantum states has attracted much attention in recent years for their potential applications in communication, computation [1], and more accurate atomic frequency standards [2]. Such quantum states with three or more particles can also display dramatic locality violation as discovered by Greenberger, Horne, and Zeilinger (GHZ) [3]. Schemes have since been proposed to produce such states based on the superposition of independent pairs of photons generated from parametric down-conversion [4,5]. Although fourphoton coincidences were measured in experiments on quantum state teleportation [6] and swapping [7], involving two independent parametric down-converters, the underlying principle is still two-photon interference. On the other hand, all of the higher-order interference schemes so far (including the GHZ multiparticle interferometry) involve only the quantum interference between two alternative paths and usually result in sinusoidal modulations in the coincidences. When more alternative paths become involved, however, new and interesting phenomena arise. For example, Shor's factorization algorithm [8] of quantum computation relies on a multiple path quantum interference effect to achieve massive parallelism. A similar effect also occurs in optical gratings. Furthermore, complete constructive or destructive quantum interference (i.e., with 100% visibility) is important for such an algorithm to yield the correct outcome with a high degree of certainty although quantum processes usually are associated with randomness.In this Letter, we report a four-photon multiple-path (six) interference effect that manifests in the partition ratio for the four photons when they arrive at a 50:50 beam splitter, two from each side. The four-photon quantum state is produced by using the stimulated emission process in a pulsed parametric down-converter. We observe a more than fivefold (theoretically, sixfold) increase in the quadruple coincidence at one exit port of the beam splitter when interference occurs. Such an increase can only be explained by the four-photon interference.It is well known by now that, when two identical photons arrive at a 50:50 beam splitter, one from each side, a two-photon interference effect occurs such that the two photons will exit together from the same side of the beam splitter [9]. This type of two-photon interference effect played an important role in the studies of nonlocality [10] a...

A prerequisite for many quantum information processing tasks to truly surpass classical approaches is an efficient procedure to encode classical data in quantum superposition states. In this work, we present a circuit-based flip-flop quantum random access memory to construct a quantum database of classical information in a systematic and flexible way. For registering or updating classical data consisting of M entries, each represented by n bits, the method requires O ( n ) qubits and O ( Mn ) steps. With post-selection at an additional cost, our method can also store continuous data as probability amplitudes. As an example, we present a procedure to convert classical training data for a quantum supervised learning algorithm to a quantum state. Further improvements can be achieved by reducing the number of state preparation queries with the introduction of quantum forking.

No abstract

Optical orthogonal frequency division multiplex (OFDM) symbol generation by all-optical discrete Fourier transform (DFT) is proposed and investigated for 100-Gbps transmission performance. We discuss a design example for a 4x25Gbps OFDM transmission system and its performance comparison with that for a 100-Gbps single-channel return-to-zero data transmission in an optically amplified system.

No abstract

We demonstrate high-resolution amplified pulse shaping using an acousto-optic modulator (AOM) at a center-wavelength of 795nm. The output pulses have energy of 200mJ/pulse and a transform-limited pulsewidth of 150fs. A spectral modulation of over 40 features is achieved in a single pulse. We characterize the pulses using the STRUT (Spectrally and Temporally Resolved Upconversion Technique). Using predistortion techniques, we demonstrate that the pulses can be shaped in amplitude and phase. We create a complex pulse shape with hyperbolic secant amplitude and hyperbolic tangent frequency sweep, which is useful for applications in adiabatic rapid passage experiments.