https://www.quantuminvestornotebook.com/ A physicist-investor's notebook on quantum computing that translates technical progress into investor-relevant judgment. en-us Fri, 30 Oct 2026 12:00:00 GMT Fri, 30 Oct 2026 12:00:00 GMT https://www.rssboard.org/rss-specification https://www.quantuminvestornotebook.com/Images/apple-touch-icon.png https://www.quantuminvestornotebook.com/ https://www.quantuminvestornotebook.com/Notes/what-is-share-dilution https://www.quantuminvestornotebook.com/Notes/what-is-share-dilution Share dilution is what happens to existing owners when a company issues new shares. Why a smaller slice is not automatically a loss, shown with numbers. Fri, 30 Oct 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/neural-decoder-real-time-edge-is-simulated https://www.quantuminvestornotebook.com/Notes/neural-decoder-real-time-edge-is-simulated Three Yonsei researchers swapped AlphaQubit's attention for a lighter Mamba design and kept its accuracy. The speed edge at today's code sizes is simulated. Thu, 29 Oct 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/data-loading-compiler-cuts-cost-on-paper https://www.quantuminvestornotebook.com/Notes/data-loading-compiler-cuts-cost-on-paper Xanadu and Rolls-Royce cut the estimated T gates for a 20 qubit fluid workflow from 2 × 10²⁰ to 9 × 10¹⁵ with cheaper data loading. Nothing ran on hardware. Thu, 29 Oct 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-the-error-correction-threshold https://www.quantuminvestornotebook.com/Notes/what-is-the-error-correction-threshold The error-correction threshold is the error rate below which bigger codes help instead of hurt. What below threshold means, and why it is not a finish line. Wed, 28 Oct 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/minecraft-grover https://www.quantuminvestornotebook.com/Notes/minecraft-grover A UIC team designed a quantum search for a Minecraft seed and tested a tiny version on IBM and Quantinuum. The full run needs 1.65 billion two qubit gates. Wed, 28 Oct 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-an-rsa-2048-resource-estimate https://www.quantuminvestornotebook.com/Notes/what-is-an-rsa-2048-resource-estimate An RSA-2048 resource estimate says how big a quantum computer must be to break RSA-2048 and how long it runs. How to read its assumptions, and why they move it. Mon, 26 Oct 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-a-cat-qubit https://www.quantuminvestornotebook.com/Notes/what-is-a-cat-qubit A cat qubit stores information in a microwave resonator so that bit flips almost never happen. How biased noise lets a line of checks replace a full grid. Sat, 24 Oct 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-q-day https://www.quantuminvestornotebook.com/Notes/what-is-q-day Q-Day is when a quantum computer could break the public-key encryption the internet relies on. What it would take, harvest now, decrypt later, and the defense. Thu, 22 Oct 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-a-decoder https://www.quantuminvestornotebook.com/Notes/what-is-a-decoder A decoder is the classical algorithm that reads error-correction alarms and bets on which errors caused them. Majority vote, matching, and why speed matters. Thu, 15 Oct 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-qaoa https://www.quantuminvestornotebook.com/Notes/what-is-qaoa QAOA, the Quantum Approximate Optimization Algorithm, writes each answer's score into phase, then uses interference to favor better ones. MaxCut as the example. Sat, 19 Sep 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-grovers-algorithm https://www.quantuminvestornotebook.com/Notes/what-is-grovers-algorithm Grover's algorithm finds a marked item among N candidates in about √N queries instead of N. The oracle's phase flip, the diffusion step, and its limits. Fri, 18 Sep 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-the-quantum-fourier-transform https://www.quantuminvestornotebook.com/Notes/what-is-the-quantum-fourier-transform The quantum Fourier transform turns patterns hidden in a state's phases into measurable outcomes, as in phase estimation and Shor's. Not simply a faster FFT. Thu, 17 Sep 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-the-ghz-state https://www.quantuminvestornotebook.com/Notes/what-is-the-ghz-state A GHZ (Greenberger-Horne-Zeilinger) state puts three or more qubits in one all-or-nothing state. How it is built and how a parity test checks its coherence. Wed, 16 Sep 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-a-bell-state https://www.quantuminvestornotebook.com/Notes/what-is-a-bell-state A Bell state is two qubits sharing one joint state. Why 00/11 correlation alone proves nothing, how a Hadamard and a CNOT build one, and the four Bell states. Tue, 15 Sep 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-an-observable https://www.quantuminvestornotebook.com/Notes/what-is-an-observable An observable is the property a quantum measurement asks about. How it differs from an outcome and an expectation value, and why estimates take many runs. Tue, 28 Jul 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-quantum-phase-estimation https://www.quantuminvestornotebook.com/Notes/what-is-quantum-phase-estimation Quantum phase estimation reads a quantity like a molecule's energy off a quantum computer by hiding it in a phase. The textbook and single-ancilla versions. Mon, 06 Jul 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-a-majorana-qubit https://www.quantuminvestornotebook.com/Notes/what-is-a-majorana-qubit A Majorana qubit splits its information across two Majorana zero modes, out of easy reach of local noise. How it is run by measurement, and why it is contested. Sun, 28 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-a-random-telegraph-signal https://www.quantuminvestornotebook.com/Notes/what-is-a-random-telegraph-signal A random telegraph signal is noise that jumps between two fixed levels as one flaw switches. How it builds 1/f noise and makes a qubit's quality drift. Sun, 28 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-the-topological-gap-protocol https://www.quantuminvestornotebook.com/Notes/what-is-the-topological-gap-protocol The topological gap protocol is Microsoft's pre-registered pass/fail test of whether a device is topological and hosts Majorana zero modes. How the test works. Sun, 28 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-the-mermin-inequality https://www.quantuminvestornotebook.com/Notes/what-is-the-mermin-inequality The Mermin inequality is a many-qubit test that proves a system is genuinely quantum when its score beats the classical limit. Why the gap grows with qubits. Tue, 23 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-a-quantum-circuit https://www.quantuminvestornotebook.com/Notes/what-is-a-quantum-circuit A quantum circuit is a recipe of gates: wires are qubits, read left to right in time, ending in measurement. Universal gate sets, width, depth and noise. Sat, 20 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-measurement https://www.quantuminvestornotebook.com/Notes/what-is-measurement Measurement turns a qubit's blend of possibilities into one definite 0 or 1. The Born rule, collapse and back-action, how readout works, and why it matters. Fri, 19 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-a-physical-qubit https://www.quantuminvestornotebook.com/Notes/what-is-a-physical-qubit A physical qubit is a real two-level quantum system built in hardware. The DiVincenzo criteria, how platforms compare, and why one is never enough on its own. Thu, 18 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-a-quantum-gate https://www.quantuminvestornotebook.com/Notes/what-is-a-quantum-gate A quantum gate is a reversible operation that changes the state of one or more qubits. Why a few gates can build any computation, and why fidelity is the wall. Wed, 17 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/the-billion-qubit-paradox https://www.quantuminvestornotebook.com/Notes/the-billion-qubit-paradox Why factoring a 2,000-bit number would take about 4,000 logical qubits and roughly a billion physical ones, and how the surface code computes with holes. Tue, 16 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-a-logical-qubit https://www.quantuminvestornotebook.com/Notes/what-is-a-logical-qubit A logical qubit is one reliable unit of quantum information spread across many fragile physical qubits. How the surface code builds it and what it costs. Mon, 15 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-entanglement https://www.quantuminvestornotebook.com/Notes/what-is-entanglement Entanglement is particles sharing one joint state with correlations stronger than anything classical. Einstein's objection, Bell's test, and why it is fragile. Sun, 14 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-superposition https://www.quantuminvestornotebook.com/Notes/what-is-superposition Superposition is a quantum system holding several possible states at once until measured. The double-slit evidence, why decoherence ends it, and why it matters. Sat, 13 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-does-fault-tolerant-mean https://www.quantuminvestornotebook.com/Notes/what-does-fault-tolerant-mean Fault tolerance: running a long quantum computation correctly even though every part is noisy. Why it goes beyond error correction, and the threshold theorem. Fri, 12 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-a-qubit https://www.quantuminvestornotebook.com/Notes/what-is-a-qubit A qubit is the basic unit of quantum information: it can be both 0 and 1 at once. How entanglement adds power, and why decoherence makes qubits hard to keep. Thu, 11 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-quantum-error-correction https://www.quantuminvestornotebook.com/Notes/what-is-quantum-error-correction Quantum error correction fixes errors in data that cannot be copied or looked at: one logical qubit across many physical ones, syndrome checks, the threshold. Wed, 10 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-qubit-connectivity https://www.quantuminvestornotebook.com/Notes/what-is-qubit-connectivity Qubit connectivity is which qubits can run a two-qubit gate directly. Why limited connectivity forces SWAP gates that add depth and noise to a circuit. Tue, 09 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-coherence-time https://www.quantuminvestornotebook.com/Notes/what-is-coherence-time Coherence time is how long a qubit holds its quantum state before noise scrambles it. T1 and T2, why decoherence causes it, and why gate speed matters too. Mon, 08 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/why-qubit-count-is-not-a-score https://www.quantuminvestornotebook.com/Notes/why-qubit-count-is-not-a-score Qubit count measures only width. Why it ignores gate fidelity, connectivity and circuit depth, and how quantum volume and volumetric benchmarks do better. Fri, 05 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/reading-a-gate-fidelity-claim https://www.quantuminvestornotebook.com/Notes/reading-a-gate-fidelity-claim A gate-fidelity number is not a full score for a quantum computer. What to ask before trusting one: which gate, measured how, on what system, at what scale. Wed, 03 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/what-is-gate-fidelity https://www.quantuminvestornotebook.com/Notes/what-is-gate-fidelity Gate fidelity measures how closely a physical quantum gate reproduces the ideal operation, and why going from 99.9% to 99.99% is a tenfold cut in error. Mon, 01 Jun 2026 12:00:00 GMT Notes https://www.quantuminvestornotebook.com/Notes/qubits-overview https://www.quantuminvestornotebook.com/Notes/qubits-overview Today's qubits come from four physics fields: atomic, solid-state, photonics and topological matter. Why the choice of physics is itself the bet being made. Thu, 21 May 2026 12:00:00 GMT Notes