# Shuntaro TakedaThe University of Tokyo | Todai · Department of Applied Physics

Shuntaro Takeda

Ph.D. in Engineering

## About

63

Publications

11,472

Reads

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2,047

Citations

Citations since 2017

Introduction

My topics of research include estimation of optical phase beyond the standard quantum limit, continuous variable quantum teleportation, quantum many-body dynamics in an ultracold Rydberg gas, and loop-based photonic quantum processor

Additional affiliations

October 2019 - present

April 2019 - September 2019

April 2017 - March 2019

## Publications

Publications (63)

We demonstrate universal and programmable three-mode linear-optical operations in the time domain by realizing a scalable dual-loop optical circuit suitable for universal quantum information processing (QIP). The programmability, validity, and deterministic operation of our circuit are demonstrated by performing nine different three-mode operations...

Optical beat-note detection with two beams at different frequencies is a key sensing technology for various spatial/temporal measurements. However, its sensitivity is inherently susceptible to shot noise due to the extra shot-noise contamination from the image band known as the 3-dB noise penalty, as well as the unavoidable optical power constraint...

One of the leading approaches to large-scale quantum information processing (QIP) is the continuous-variable (CV) scheme based on time multiplexing (TM). As a fundamental building block for this approach, quantum light sources to sequentially produce time-multiplexed squeezed-light pulses are required; however, conventional CV TM experiments have u...

Universal multi-mode linear optical operations are essential for almost all optical quantum information protocols (QIPs) for both qubits and continuous variables. Thus far, large-scale implementation of such operations has been pursued mainly by developing photonic chips that contain large interferometers for path-encoded optical modes. However, su...

One of the leading approaches to large-scale quantum information processing (QIP) is the continuous-variable (CV) scheme based on time multiplexing (TM). As a fundamental building block for this approach, quantum light sources to sequentially produce time-multiplexed squeezed-light pulses are required; however, conventional CV TM experiments have u...

Non-Gaussian states are essential for many optical quantum technologies. The so-called optical quantum state synthesizer (OQSS), consisting of Gaussian input states, linear optics, and photon-number resolving detectors, is a promising method for non-Gaussian state preparation. However, an inevitable and crucial problem is the complexity of the nume...

Variational quantum algorithms (VQAs) provide a promising approach to achieving quantum advantage for practical problems on near-term noisy intermediate-scale quantum (NISQ) devices. Thus far, intensive studies on qubit-based VQAs have been made theoretically and experimentally on several physical platforms. However, there have been much fewer theo...

We demonstrate a universal multi-mode linear optical quantum operation in the time domain using a scalable and programmable dual-loop-based optical circuit. This work holds great promise for time-multiplexed large-scale optical quantum information processing.

We demonstrate a time-multiplexed squeezed light source, which can programmably choose each squeezing level and direction of the output sequential squeezed-state pulses and is thus essential for large-scale quantum information processing in the time domain.

We demonstrate a continuous-variable version of the quantum approximate optimization algorithm on a programmable single-mode photonic quantum computer, minimizing one-variable continuous functions. The results highlight the potential of continuous-variable quantum computing in near-term applications.

A quantum processor to import, process, and export optical quantum states is a common core technology enabling various photonic quantum information processing. However, there has been no photonic processor that is simultaneously universal, scalable, and programmable. Here, we report on an original loop-based single-mode versatile photonic quantum p...

Realizing a large-scale quantum computer requires hardware platforms that can simultaneously achieve universality, scalability, and fault tolerance. As a viable pathway to meeting these requirements, quantum computation based on continuous-variable optical systems has recently gained more attention due to its unique advantages and approaches. This...

Non-Gaussian states are essential for many quantum technologies with continuous variables. The so-called optical quantum state synthesizer (OQSS), consisting of Gaussian input states, linear optics, and photon-number resolving detectors, is a promising method for non-Gaussian state preparation. However, an inevitable and crucial problem is the comp...

We develop a loop-based single-mode photonic quantum processor and demonstrate its gate operations. Showing its programmability, scalability, and potential universality, the results indicate our processor is suitable for general-purpose applications.

An array of ultracold atoms in an optical lattice (Mott insulator) excited to a state where single electron wave-functions spatially overlap would represent a new and ideal platform to simulate exotic electronic many-body phenomena in the condensed phase. However, this highly excited non-equilibrium system is expected to be so short-lived that it h...

Generating large-scale cluster states
The development of a practical quantum computer requires universality, scalability, and fault tolerance. Although much progress is being made in circuit platforms in which arrays of qubits are addressed and manipulated individually, scale-up of such systems is experimentally challenging. Asavanant et al. and La...

We experimentally demonstrate storage and on-demand release of phase-sensitive, photon-number superposition states of the form α|0⟩+βeiθ|1⟩ for an optical quantized oscillator mode. For this purpose, we newly developed a phase-probing mechanism compatible with a storage system composed of two concatenated optical cavities, which was previously empl...

Photonic quantum computing is one of the leading approaches to universal quantum computation. However, large-scale implementation of photonic quantum computing has been hindered by its intrinsic difficulties, such as probabilistic entangling gates for photonic qubits and lack of scalable ways to build photonic circuits. Here, we discuss how to over...

Quantum information protocols require various types of entanglement, such as Einstein-Podolsky-Rosen, Greenberger-Horne-Zeilinger, and cluster states. In optics, on-demand preparation of these states has been realized by squeezed light sources, but such experiments require different optical circuits for different entangled states, thus lacking vers...

Photonic quantum computing is one of the leading approaches to universal quantum computation. However, large-scale implementation of photonic quantum computing has been hindered by its intrinsic difficulties, such as probabilistic entangling gates for photonic qubits and lack of scalable ways to build photonic circuits. Here we discuss how to overc...

Optical quantum states defined in temporal modes, especially non-Gaussian states, such as photon-number states, play an important role in quantum computing schemes. In general, the temporal mode structures of these states are characterized by one or more complex functions called temporal mode functions (TMFs). Although we can calculate the TMF theo...

Quantum computation promises applications that are thought to be impossible with classical computation. To realize practical quantum computation, the following three properties will be necessary: universality, scalability, and fault-tolerance. Universality is the ability to execute arbitrary multi-input quantum algorithms. Scalability means that co...

Optical quantum states defined in temporal modes, especially non-Gaussian states like photon-number states, play an important role in quantum computing schemes. In general, the temporal-mode structures of these states are characterized by one or more complex functions called temporal-mode functions (TMFs). Although we can calculate TMF theoreticall...

We demonstrate on-demand generation of photonic entanglement by dynamically controlling a loop-based circuit at nanosecond timescale. We generate 6 types of entangled states including 1000-mode 1D-cluster states without changing the circuit architecture.

Quantum information protocols require various types of entanglement, such as Einstein-Podolsky-Rosen (EPR), Greenberger-Horne-Zeilinger (GHZ), and cluster states. In optics, on-demand preparation of these states has been realized by squeezed light sources, but such experiments require different optical circuits for different entangled states, thus...

We experimentally demonstrate storage and on-demand release of phase-sensitive, photon-number superposition states of the form $\alpha |0\rangle + \beta e^{i\theta} |1\rangle$ for an optical quantized oscillator mode. For this purpose, we introduce a phase-probing mechanism to a storage system composed of two concatenated optical cavities, which wa...

We propose a method to subtract a photon from a double sideband mode of continuous-wave light. The central idea is to use phase modulation as a frequency sideband beam splitter in the heralding photon subtraction scheme, where a small portion of the sideband mode is down-converted to 0 Hz to provide a trigger photon. An optical cat state is created...

Frequency multiplexing allows us to encode multiple quantum states on a single light beam. Successful multiplexing of Gaussian and non-Gaussian states potentially leads to scalable quantum computing or communication. Here we create an optical Schr\"odinger's cat state at a 500.6MHz sideband, as a first step to non-Gaussian, frequency-division multi...

We demonstrate a programmable optical quantum gate with a 25ns-latency digital feedforward. Such a flexible, stable, and fast feedforward enables large-scale universal continuous-variable quantum computation in time domain.

We propose a scalable scheme for optical quantum computing using continuous-variable quantum gates in a loop-based architecture. This architecture offers a universal gate set for both qubits and continuous variables with almost minimum resources.

We propose and demonstrate a method useful to characterize optical multi-temporal-mode Fock states typified by quantum error correction code states using a simple experimental setup and data analysis procedure.

We demonstrate an optical quantum nondemolition (QND) interaction gate with a bandwidth of about 100 MHz. Employing this gate, we are able to perform QND measurements in real time on randomly fluctuating signals. Our QND gate relies upon linear optics and offline-prepared squeezed states. In contrast to previous demonstrations on narrow sideband mo...

We propose an experimental scheme to generate, in a heralded fashion, arbitrary quantum superpositions of two-mode optical states with a fixed total photon number $n$ based on weakly squeezed two-mode squeezed state resources (obtained via weak parametric down conversion), linear optics, and photon detection. Arbitrary $d$-level (qudit) states can...

We propose general methodology of deterministic single-mode quantum interaction nonlinearly modifying single quadrature variable of a continuous variable system. The methodology is based on linear coupling of the system to ancillary systems subsequently measured by quadrature detectors. The nonlinear interaction is obtained by using the data from t...

We propose a scalable scheme for optical quantum computing using measurement-induced continuous-variable quantum gates in a loop-based architecture. Here, time-bin-encoded quantum information in a single spatial mode are deterministically processed in a nested loop by an electrically programmable gate sequence. This architecture can process any inp...

We theoretically investigate many-body systems with long range interactions in ensembles of Rydberg atoms undergoing dynamics described by an Ising-type Hamiltonian. The interactions are found to strongly modify both the contrast and phase of the population signal monitored via the double-pulse Ramsey interferometry technique. We find analytical ex...

A single quantum particle can be described by a wavefunction that spreads
over arbitrarily large distances, but it is never detected in two (or more)
places. This strange phenomenon is explained in quantum theory by what Einstein
repudiated as "spooky action at a distance": the instantaneous nonlocal
collapse of the wavefunction to wherever the par...

Hybrid quantum teleportation – continuous-variable teleportation of qubits – is a promising approach for deterministically teleporting photonic
qubits. We propose how to implement it with current technology. Our theoretical model shows that faithful qubit transfer can be achieved for this teleportation by choosing an optimal gain for the teleporte...

We experimentally realize "hybrid" entanglement swapping between
discrete-variable (DV) and continuous-variable (CV) optical systems. DV
two-mode entanglement as obtainable from a single photon split at a beam
splitter is robustly transferred by means of efficient CV entanglement and
operations, using sources of squeezed light and homodyne detectio...

We experimentally demonstrate the noiseless teleportation of a single photon
by conditioning on quadrature Bell measurement results near the origin in phase
space and thereby circumventing the photon loss that otherwise occurs even in
optimal gain-tuned continuous-variable quantum teleportation. In general,
thanks to this loss suppression, the nois...

Historically, two complementary approaches to optical quantum information
processing have been pursued: qubits and continuous-variables, each exploiting
either particle or wave nature of light. However, both approaches have pros and
cons. In recent years, there has been a significant progress in combining both
approaches with a view to realizing hy...

We demonstrate the nonlocal wavefunction collapse for a single particle, the idea of which dates back to Einstein's first argument on his concerns about quantum theory, by performing EPR-steering using heralded single photons.

We experimentally demonstrate bolstering the strength of gain-tuned continuous variable quantum teleportation of a single photon by conditioning on the sender's measurement results to eliminate excess vacuum contamination in the output.

We experimentally demonstrate continuous-variable quantum teleportation of discrete-variable entanglement in the form of a split single photon. Entanglement is optimally transferred for finite resource squeezing by tuning the teleporter's feedforward gain.

We present a general formalism to describe continuous-variable (CV) quantum
teleportation of discrete-variable (DV) states with gain tuning, taking into
account experimental imperfections. Here the teleportation output is given by
independently transforming each density matrix element of the initial state.
This formalism allows us to accurately mod...

Quantum teleportation allows for the transfer of arbitrary unknown quantum states from a sender to a spatially distant receiver, provided that the two parties share an entangled state and can communicate classically. It is the essence of many sophisticated protocols for quantum communication and computation. Photons are an optimal choice for carryi...

Quantum teleportation allows for the transfer of arbitrary, in principle, unknown quantum states from a sender to a spatially distant receiver, who share an entangled state and can communicate classically. It is the essence of many sophisticated protocols for quantum communication and computation. In order to realize flying qubits in these schemes,...

Keeping Track of Photon Phase
In optical interferometers or optical communications, information is often stored in terms of the phase of the waveform or light pulse. However, fluctuations and noise can give rise to random jitter in the phase and amplitude of the optical pulses, making it difficult to keep track of the phase. Yonezawa et al. (p. 151...

We experimentally generate arbitrary time-bin qubits using continuous-wave
light. The advantage unique to our qubit is its compatibility with
deterministic continuous-variable quantum information processing. This
compatibility comes from its optical coherence with continuous waves,
well-defined spatio-temporal mode, and frequency spectrum within th...

We demonstrate an effective mode-filtering technique to obtain robust non-Gaussian states by removing their noisy low-frequency components. Mode-filtered states outperform conventional states in the robust implementation of quantum teleportation.

We propose and demonstrate an effective mode-filtering technique of
non-Gaussian states generated by photon-subtraction. More robust non-Gaussian
states have been obtained by removing noisy low frequencies from the original
mode spectrum. We show that non-Gaussian states preserve their non-classicality
after quantum teleportation to a higher degree...

We experimentally demonstrate conditional teleportation of non-Gaussian nonclassical states of light. The nonclassicality of the Wigner function is proven to be enhanced: the negativity is stronger than what deterministic operations achieve.

We develop a simple and efficient theoretical model to understand the quantum properties of broadband continuous variable quantum teleportation. We show that, if stated properly, the problem of multimode teleportation can be simplified to teleportation of a single effective mode that describes the input state temporal characteristic. Using that mod...

We develop a simple and efficient theoretical model to understand the quantum properties of broadband con-tinuous variable quantum teleportation. We show that, if stated properly, the problem of multimode teleportation can be simplified to teleportation of a single effective mode that describes the input state temporal characteristic. Using that mo...

We demonstrate teleportation of Schrödinger's cat wave-packets of light in a fully quantum regime. To further increase non-classicality of operations we propose two improvements: wave-packet frequency mode-matching; conditional teleportation.

We demonstrate squeezing-enhanced adaptive optical phase estimation for a stochastically varying phase. By using a continuous-wave phase squeezed beam, estimation accuracy is improved by a factor of 1.4 compared to a coherent beam case.

We report on the experimental quantum teleportation of strongly nonclassical
wave packets of light. To perform this full quantum operation while preserving
and retrieving the fragile non-classicality of the input state, we have
developed a broadband, zero-dispersion teleportation apparatus that works in
conjunction with time-resolved state preparat...

We experimentally prepare non-classical states of light with negative
Wigner function and perform continuous variable quantum teleportation of
these states. We develop an analytical model that encompass the two main
aspects of this experiment, multimode wave-packet teleportation and
negativity teleportation. We present experimental results and comp...