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Sinan Bugu

Publications and source records attributed to Sinan Bugu.

12 recordsLinked to original sources
arXiv2026

Beyond Single-Shot Fidelity: Chernoff-Based Throughput Optimization in Superconducting Qubit Readout

Single-shot fidelity is the standard benchmark for superconducting qubit readout, yet it does not directly minimize the wall-clock time needed to certify a quantum state. We treat the dispersive measurement record as a stochastic communication channel and compute the classical Chernoff information governing the multi-shot error exponent, using a trajectory model that incorporates T1 relaxation with full cavity memory. The integration time that maximizes single-shot fidelity and the time that minimizes total certification time do not coincide. For representative transmon parameters and hardware overheads, the throughput-optimal window is longer, cutting certification time by roughly 9-11%, with the gain saturating near 1.13x in the high-readout-power and high-overhead regime. Benchmarking the extracted classical information against the unit-efficiency Gaussian Chernoff limit defines an information-extraction efficiency: dispersive schemes capture ~45% at short integration times, dropping to eta_info(tau_rate) ~ 12% at tau_rate ~ 1.22 us as T1-induced trajectory smearing accumulates. These results connect readout calibration directly to the operational objective of minimizing certification time in high-throughput superconducting processors.

quant-ph↗
arXiv2026

Payoff-Free Coordination Reveals Hidden Quantum Correlation Structure

We study decentralized multi-agent coordination where agents must correlate actions against an unobserved field and cannot communicate. To isolate correlation geometry from payoff optimization, we introduce the Hidden-Field Coordination (HFC) model, which enforces identical information access and no-signaling constraints across strategies. Using information-theoretic diagnostics, we compare classical shared-randomness baselines with an entanglement-mediated strategy based on multipartite W states and a strictly local Spontaneous Leader Election rule. Within the restricted symmetric shared-latent baseline studied here, increasing total correlation is achieved primarily by driving actions toward alignment (copying), which also increases pairwise coincidence (collisions). By contrast, the quantum strategy realizes a collision-suppressing coordination regime: it preserves global dependence while reducing pairwise coincidence below the independent (product) baseline induced by the common marginal distribution. This produces a geometric separation in the joint-action distribution. Classical baselines concentrate probability near the diagonal of action equality, whereas the entanglement-mediated mapping occupies an offset-diagonal region associated with relational roles. Accordingly, the entanglement signature in this setting is not higher correlation magnitude; total-correlation differentials can be negative relative to the classical copying optimum. Instead, it reflects a change in dependence geometry that supports robust anti-coordination.

quant-ph↗
arXiv2025

Resilience of Entanglement-Induced Coordination in Adversarial Environments: The Team-Based Quantum Sabotage Game

Quantumgametheoryextendsclassical strategic decision-making by incorporating quantum superposition, entanglement, and measurement-induced randomness into competitive interactions. This paper introduces a team-based Quantum Sabotage Game (QSG), in which classical and quantum-enhanced teams engage in adversarial decision-making under identical information constraints. Unlike baseline classical teams, whose members act independently, quantum teams employ entanglement-assisted coor dination, generating structured correlations among decentralized actions without classical communication. We develop a formal quantum game-theoretic framework and analyze multi-agent strategies using Bell and Wentangled states, benchmarked against size-equivalent classical teams. Using numerical simulations, we compare outcome distributions, correlation structure, and robustness under ideal conditions, standard quantum noise models, and a device-inspired, reproducible hardware-like noise model via the Qiskit Aer FakeKyiv backend. While the symmetric payoff structure precludes any asymptotic increase in expected utility, multipartite entanglement, particularly W-state correlations, reshapes the finite-run joint-action distribution, producing nonclassical coordination patterns rather than an expectation-value advantage. These patterns persist under realistic noise, demonstrating that the resulting correlation signatures remain observable and differ from those produced by independent classical sampling. These results clarify the operational role of entanglement in adversarial environments, distinguishing correlation-based coordination from expectation-value advantage, and establish the Quantum Sabotage Game as a testbed for studying noise-resilient multi-agent quantum decision-making.

quant-ph↗
arXiv2024

High fidelity TiN processing modes for multi-gate Ge-based quantum devices

Charge or spin-qubits can be realized by using gate-defined quantum dots (QDs) in semiconductors in a similar fashion to the processes used in CMOS for conventional field-effect transistors or more recent fin FET technology. However, to realize larger number of gate-defined qubits, multiples of gates with ultimately high resolution and fidelity is required. Electron beam lithography (EBL) offers flexible and tunable patterning of gate-defined spin-qubit devices for studying important quantum phenomena. While such devices are commonly realized by a positive resist process using metal lift-off, there are several clear limitations related to the resolution and the fidelity of patterning. Herein, we report a systematic study of an alternative TiN multi-gates definition approach based on the highest resolution hydrogen silsesquioxane (HSQ) EBL resist and all associated processing modes. The TiN gate arrays formed show excellent fidelity, dimensions down to 15 nm, various densities, and complexities. The processing modes developed were used to demonstrate applicability of this approach to forming multi-gate architectures for two types of spin-qubit devices prototypic to i) NW/fin-type FETs and ii) planar quantum well-type devices, both utilizing epi-grown Ge device layers on Si, where GeSn or Ge are the host materials for the QDs.

cond-mat.mes-hall↗
arXiv2021

Deterministic preparation of W states via spin-photon interactions

Spin systems such as silicon or nitrogen vacancy centers in diamond, quantum dots and quantum dot molecules coupled to optical cavities appear as key elements for creating quantum networks as not only constituting the nodes of the network, but also assisting the creation of photonic networks. Here we study deterministic preparation of arbitrary size $W$ states with spin systems. We present an efficient operation on three qubits, two being the logical qubits and one being the ancillary qubit, where no interaction between the logical qubits are required. The proposed operation can create a $W$-type Einstein-Podolsky-Rosen (EPR) pair from two separable qubits, and expand that EPR pair or an arbitrary size $W$ state by one, creating a $W$-like state. Taking this operation as the fundamental building block, we show how to create a large scale $W$ state out of separable qubits, or double the size of a $W$ state. Based on this operation and focusing on nitrogen vacancy (NV) centers in diamond as an exemplary spin system, we propose a setup for preparing $W$ states of circularly polarized photons, assisted by a single spin qubit, where no photon-photon interactions are required. Next, we propose a setup for preparing $W$ states of spin qubits of spatially separated systems, assisted by a single photon. We also analyze the effects of possible imperfections in implementing the gates on the fidelity of the generated $W$ states. In our setups, neither post-measurement, nor post-processing on the states of spin or photonic qubit is required. Our setups can be implemented with current technology, and we anticipate that they contribute to quantum science and technologies.

quant-ph↗
arXiv2021

4.2 K Sensitivity-Tunable Radio Frequency Reflectometry of a Physically Defined P-channel Silicon Quantum Dot

We demonstrate the measurement of p-channel silicon-on-insulator quantum dots at liquid helium temperatures by using a radio frequency (rf) reflectometry circuit comprising of two independently tunable GaAs varactors. This arrangement allows observing Coulomb diamonds at 4.2\,K under nearly best matching condition and optimal signal-to-noise ratio. We also discuss the rf leakage induced by the presence of the large top gate in MOS nanostructures and its consequence on the efficiency of rf-reflectometry. These results open the way to fast and sensitive readout in multi-gate architectures, including multi-qubit platforms.

cond-mat.mes-hall↗
arXiv2020

Surpassing the Classical Limit in Magic Square Game with Distant Quantum Dots Coupled to Optical Cavities

The emergence of quantum technologies is heating up the debate on quantum supremacy, usually focusing on the feasibility of looking good on paper algorithms in realistic settings, due to the vulnerability of quantum systems to myriad sources of noise. In this vein, an interesting example of quantum pseudo-telepathy games that quantum mechanical resources can theoretically outperform classical resources is the Magic Square game (MSG), in which two players play against a referee. Due to noise, however, the unit winning probability of the players can drop well below the classical limit. Here, we propose a timely and unprecedented experimental setup for quantum computation with quantum dots inside optical cavities, along with ancillary photons for realizing interactions between distant dots to implement the MSG. Considering various physical imperfections of our setup, we first show that the MSG can be implemented with the current technology, outperforming the classical resources under realistic conditions. Next, we show that our work gives rise to a new version of the game. That is, if the referee has information on the physical realization and strategy of the players, he can bias the game through filtered randomness and increase his winning probability. We believe our work contributes to not only quantum game theory, but also quantum computing with quantum dots.

quant-ph↗
arXiv2020

RF Reflectometry for Readout of Charge Transition in a Physically Defined PMOS Silicon Quantum Dot

We have embedded a physically defined p-channel silicon MOS quantum dot (QD) device into an impedance transformer RC circuit. To decrease the parasitic capacitance and surpass the cutoff frequency of the device which emerges in MOS devices that have a top gate and act as RC low-pass filter, we fabricate a new device to reduce the device's top gate area from 400 $\mbox{$\mu$m}^2$ to 0.09 $\mbox{$\mu$m}^2$. Having a smaller top gate eliminates the cutoff frequency problem preventing the RF signal from reaching QD. We show that we have fabricated a single QD properly, which is essential for RF single-electron transistor technique. We also analyze and improve the impedance matching condition and show that it is possible to perform readout of charge transition at 4.2 K by RF reflectometry, which will get us to fast readout of charge and spin states.

cond-mat.mes-hall↗
arXiv2016

Deterministic Local Expansion of W States

In large quantum systems multipartite entanglement can be found in many inequivalent classes under local operations and classical communication. Preparing states of arbitrary size in different classes is important for performing a wide range of quantum protocols. W states, in particular, constitute a class with a variety of quantum networking protocols. However, all known schemes for preparing W states are probabilistic, with resource requirements increasing at least sub-exponentially. We propose a deterministic scheme for preparing W states that requires no prior entanglement and can be performed locally. We introduce an all-optical setup that can efficiently prepare W states of arbitrary size. Our scheme advances the use of W states in real-world quantum networks and could be extended to other physical systems.

quant-ph↗
arXiv2014

Fusing multiple W states simultaneously with a Fredkin gate

We propose an optical scheme to prepare large-scale entangled networks of W states. The scheme works by simultaneously fusing three polarization-encoded W states of arbitrary size via accessing only one qubit of each W state. It is composed of a Fredkin gate (controlled-swap gate), two fusion gates [as proposed in New J. Phys. 13, 103003 (2011)] and an H-polarized ancilla photon. Starting with three $n$-qubit W states, the scheme prepares a new W state with $3(n-1)$-qubits after postselection if both fusion gates operate successfully, i.e. a four-fold coincidence at the detectors. The proposed scheme reduces the cost of creating arbitrarily large W states considerably when compared to previously reported schemes.

quant-ph↗
arXiv2013

Enhancing the W State Quantum Network Fusion Process with A Single Fredkin Gate

Integrating a single Fredkin (controlled swap) gate to the previously introduced W state fusion mechanism (Ozdemir et al, N. J. Phys. 13, 103003, 2011) and using an ancillary photon, we increase the size of the fused W states and essentially, we improve the success probability of the fusion process in a promising way for a possible deterministic W state fusion mechanism. Besides fusing arbitrary size W states, our setup can also fuse Bell states to create W states with a success probability 3/4 which is much higher than the previous works. Therefore using only this setup, it is now possible to start with Bell pairs to create and expand arbitrary size W states. Since higher probability of success implies a lower cost of resource in terms of the number of the states spent to achieve a target size, our setup gives rise to more cost-efficient scenarios.

quant-ph↗