Speaker 1: Welcome to the quart Side. Quantum Physics Podcast, an exploration
Speaker 1: of the fundamental structure of reality, where quantum laws govern matter, energy,
Speaker 1: and information. Here, uncertainty is a feature, not a flaw,
Speaker 1: and understanding begins at the smallest scales.
Speaker 2: Imagine a machine that uh well manages to perfectly remember
Speaker 2: absolutely everything that has ever happened to it.
Speaker 3: Right, like, every single input, every tiny fluctuation.
Speaker 2: Exactly every interaction. But while it's doing that, simultaneously, at
Speaker 2: the exact same moment, it completely forgets its entire past.
Speaker 2: Oh wow, Yeah, it's entirely wipe clean. But you know,
Speaker 2: it somehow holds onto a perfect diary of everything. It
Speaker 2: sounds like a broken hard drive or I don't know,
Speaker 2: philosophical riddle.
Speaker 3: It sounds like a severe violation of causality. Honestly, I
Speaker 3: mean it directly contradicts how we experience the flow of time,
Speaker 3: and which is the basic mechanics of cause and effect.
Speaker 3: Because if a system remembers, then the past dictates its present,
Speaker 3: and if it forgets, only the present matters. You just
Speaker 3: you can't have both.
Speaker 2: But it turns out that impossible contradiction is exactly how
Speaker 2: reality operates at the most fundamental level. It really is,
Speaker 2: and that's what we're unpacking today. We're looking at this massive,
Speaker 2: honestly mind bending breakthrough in quantum physics. From April fourteenth,
Speaker 2: twenty twenty six, researchers publish these findings in prx Quantum,
Speaker 2: proving that quantum systems can serely remember their history from
Speaker 2: one specific mathematical perspective.
Speaker 3: While appearing totally, completely, one hundred percent memoryless from another.
Speaker 2: Yeah, which is just wild. It's this fundamental property of
Speaker 2: nature that we simply hadn't realized was there.
Speaker 3: And the implications here are enormous for you listening, because
Speaker 3: you know this isn't just theoretical philosophy. It's a mathematically
Speaker 3: proven discovery.
Speaker 2: Right, It's actual hard science.
Speaker 3: Exactly, and this to basically rewrite the blueprint for the
Speaker 3: next generation of quantum technologies. We are talking about the
Speaker 3: architecture of quantum computers, the sensitivity of microscopic sensors, and
Speaker 3: even the foundation of ultra scure communications.
Speaker 2: So our mission today is to tear this concept down
Speaker 2: to the studs basically and figure out the actual mechanics
Speaker 2: of how the universe pulls off this magic.
Speaker 3: Trick without the dense jargon exactly.
Speaker 2: No dense jargon. We want you to understand exactly why
Speaker 2: reality at the smallest scale is far more flexible than
Speaker 2: we ever thought. And to get there, we need to
Speaker 2: establish what memory actually means in physics.
Speaker 3: Right, because it's not like human memory.
Speaker 2: No, not at all. Let's use let's use the classic
Speaker 2: broken glass analogy to ground this. So in everyday classical physics,
Speaker 2: the physics of big things, you interact with baseballs and
Speaker 2: coffee mugs.
Speaker 3: The macroscopic world.
Speaker 2: Right, if you drop a glass and it shatters, the
Speaker 2: future state of that glass depends entirely on the fact
Speaker 2: that it broke. The glass essentially remembers the impact.
Speaker 3: Yeah, that's a perfect macroscopic view. But when physicists model
Speaker 3: classical systems mathematically, they actually often try to simplify them
Speaker 3: into what we call Markovian processes. Okay, Markovian right, And
Speaker 3: a Markovian system is basically the ultimate goldfish of the
Speaker 3: physical world.
Speaker 2: The goldfish, I love that it.
Speaker 3: Has zero memory none. Its future behavior is dictated strictly
Speaker 3: by its exact state at this current nanosecond.
Speaker 2: So the past just doesn't factor in at all.
Speaker 3: Exactly. It doesn't matter if, say, a baseball was thrown
Speaker 3: by a pitcher or shot out of a cannon. If
Speaker 3: you know it's current velocity, its position, and the wind
Speaker 3: resistance right now, you know exactly where it will land.
Speaker 2: The history is completely irrelevant to the trajectory exactly.
Speaker 3: But when we move down to the quantum realm, things
Speaker 3: get significantly.
Speaker 2: More complicated because things get messy.
Speaker 3: Very messy. We are rarely dealing with perfectly isolated quantum
Speaker 3: systems floating in some undisturbed vacuum. We're dealing with what
Speaker 3: we call open quantum systems.
Speaker 2: Because in a real laboratory, or I mean inside an
Speaker 2: actual quantum computer that engineers are trying to build, these
Speaker 2: particles are constantly interacting with their environment right right. They're
Speaker 2: bathed in electromagnetic radiation, subjected to tiny thermal fluctuations, bumping
Speaker 2: into stray photons. It's a chaotic neighborhood.
Speaker 3: And that environmental interaction is the key to all of this,
Speaker 3: because when an open quantum system interacts with its environment,
Speaker 3: it entangles with it, It gets tied up with it, exactly.
Speaker 3: Information about the quantum system physically leaks out into the
Speaker 3: surrounding environment. Now, if the environment is just massive and chaotic.
Speaker 3: That information might just dissipate forever, just lost in the noise, right,
Speaker 3: and that would be a Markovian memoryless process. But often
Speaker 3: the environment acts a bit more like a sponge. It
Speaker 3: absorbs the information, holds onto it, and eventually that information
Speaker 3: backflows into the quantum system.
Speaker 2: Oh wow, so the system gets like a delayed echo
Speaker 2: of its own passed.
Speaker 3: That is the exact mechanism I'm talking about. Because the
Speaker 3: past state of the system altered the environment, and now
Speaker 3: the environment is altering the present system.
Speaker 2: So the system effectively has memory.
Speaker 3: Yes, and we call this a non Markovian process. The
Speaker 3: past actively and persistently influences the future through this environmental backflow.
Speaker 2: Okay, let's unpack this because here is where the plot
Speaker 2: really thickens for you listening. If we know open quantum
Speaker 2: systems have this backflow, this memory, how do physicists actually
Speaker 2: track or measure that? That is the big question, because
Speaker 2: you can't just slap a GPS tracking device on an
Speaker 2: electron's past. We have to use mathematical frameworks to model
Speaker 2: the evolution. And in quantum mechanics, we essentially have two
Speaker 2: foundational lenses to view reality.
Speaker 3: Right, The two pictures.
Speaker 2: Yeah, the Schrodinger picture and the Heisenberg.
Speaker 3: Picture, right, And these are the two primary mathematical formulations
Speaker 3: we use to predict the outcomes of any quantum experiment.
Speaker 3: So in the Schrodinger picture, we focus on the quantum state.
Speaker 2: Of the system, which is often represented by a density.
Speaker 3: Matrix exactly, but conceptually, just think of the state as
Speaker 3: a highly complex probability cloud that describes all the potential
Speaker 3: outcomes of a measurement. In this picture, that probability cloud
Speaker 3: is dynamic. It's moving, right, It's constantly morphing, waving and
Speaker 3: evolving as time ticks forward. Meanwhile, the mathematical operators, the
Speaker 3: things representing the actual physical measurements we might take like
Speaker 3: position or momentum or spin, those remain entirely static.
Speaker 2: They just sit there while the cloud dances around them. Basically,
Speaker 2: and the Heisenberg picture is the exact inverse of that.
Speaker 3: Correct. So in the Heisenberg formulation, the quantum state, that
Speaker 3: probability cloud is totally locked in place. It represents the
Speaker 3: initial conditions and it never changes. Okay, Instead, the measurement
Speaker 3: operators themselves evolve over time.
Speaker 2: Okay, let's try an analogy to visualize the mechanics here,
Speaker 2: because this is notorious for tripping people up. Let's think
Speaker 2: about two friends watching a movie.
Speaker 3: Oh I like where this is going, right.
Speaker 2: So let's say Friend A is watching the movie using
Speaker 2: the Schrodinger picture. They are watching the full story unfold
Speaker 2: seen by scene. They see the characters make decisions, they
Speaker 2: see the consequences. They see a clear narrative with cause
Speaker 2: and effect.
Speaker 3: They see the memory of the plot exactly.
Speaker 2: They see clear memory. But Friend B is using the
Speaker 2: Heisenberg picture. They aren't watching the continuous movie. They only
Speaker 2: see quick, isolated snapshots of the character's actions, completely out
Speaker 2: of context, just random frames. So Friend B thinks the
Speaker 2: story has absolutely no connection to the past. It's just
Speaker 2: random stuff happening. Both friends are watching the exact same movie,
Speaker 2: the exact same physical system, but experiencing memory completely differently.
Speaker 3: That's a really great way to visualize how two perspectives
Speaker 3: can fundamentally disagree on what is happening. And what's fascinating
Speaker 3: is that for decades, memory was treated as a simple
Speaker 3: yes or no.
Speaker 2: Property either had memory or it didn't.
Speaker 3: Right, physicists assumed that if ays had a clear historical trend,
Speaker 3: both frameworks both the Schrodinger and Heisenberg lenses would undeniably
Speaker 3: reflect that memory. Memory was considered an absolute objective property
Speaker 3: of the system itself, which.
Speaker 2: Brings us to the discovery from April twenty twenty six. Yeah,
Speaker 2: because what happens when friend A and friend B violently
Speaker 2: disagree on whether a system has memory or not. So
Speaker 2: this research team, led by Federico Sedemo and Jerkiapilo from
Speaker 2: the University of Turku, along with colleagues from the University
Speaker 2: of Milan and Nicholas Copernicus University, they decided to rigorously
Speaker 2: stress test this assumption.
Speaker 3: And they didn't just ask philosophical questions about this. They
Speaker 3: dug into the hard math of what we call dynamical maps.
Speaker 2: Okay, let's define a dynamical map, because that is basically
Speaker 2: the engine of this entire discovery.
Speaker 3: Yeah. A dynamical map is basically the official mathematical rule book.
Speaker 3: It dictates how an open quantrum system changes from state
Speaker 3: A to state B over a specific period of time. Okay,
Speaker 3: When researchers want to test if the system has memory,
Speaker 3: if it's marek Kovian or non Markovian, they test this
Speaker 3: dynamical map for a property called divisibility.
Speaker 2: Divisibility, yeah, meaning you can chop the timeline up into
Speaker 2: independent chumps exactly. So like, if a process takes ten seconds,
Speaker 2: can I mathematically calculate the jump from second three to
Speaker 2: second four without needing to know anything about seconds one
Speaker 2: and two.
Speaker 3: That's the core of it.
Speaker 2: Yes, yeah.
Speaker 3: Technically they test if the map can be decomposed into
Speaker 3: a sequence of completely positive trace preserving maps, but conceptually,
Speaker 3: if it can be perfectly sliced up into these independent
Speaker 3: intermediate steps, the process is divisible, meaning the system is Markovian, right,
Speaker 3: it has no memory, it's the goldfish. But if the
Speaker 3: math breaks down and you actually can't slice it into
Speaker 3: independent steps without violating the physical rules of quantum mechanics.
Speaker 2: Which means the intermediate step requires information from the past
Speaker 2: to even make sense.
Speaker 3: Exactly, then the map is indivisible. The system is non Markovian,
Speaker 3: it has memory.
Speaker 2: Okay, here's where it gets really interesting, but also where
Speaker 2: I need to push back on the MA a bit. Sure.
Speaker 2: So the Turku team looks at a system through the
Speaker 2: Schrodinger picture the evolving state, and they test the dynamical map,
Speaker 2: and the math says it is perfectly divisible. It's a goldfish.
Speaker 2: It has no memory. Right, But then they calculate the
Speaker 2: dynamical map for the Heisenberg observables, and suddenly the math
Speaker 2: says it is indivisible. It has memory. But wait, if
Speaker 2: a system looks memoryless in the Schrodinger picture, isn't that
Speaker 2: just a math trick?
Speaker 3: It really isn't.
Speaker 2: But how does it actually secretly keep a diary? Both
Speaker 2: pictures have to yield the exact same physical predictions in
Speaker 2: the lab. Right, how can the same physical system simultaneously
Speaker 2: fail and pass the test for memory?
Speaker 3: It feels like a contradiction because we are so used
Speaker 3: to thinking of memory as an object you hold, rather
Speaker 3: than a dynamic relationship. To understand how this happens, we
Speaker 3: have to look at what the Schrodinger picture actually does
Speaker 3: to the environment. Mathematically, when you calculate the evolving state
Speaker 3: in the Schrodinger picture, you have to perform operation called
Speaker 3: tracing out the environmental degrees of freedom.
Speaker 2: Tracing out you basically take the infinitely complex environment and
Speaker 2: average it down into a workable probability.
Speaker 3: Yes, you mathematically average over all the chaotic monks, the
Speaker 3: stray photons, the thermal noise. By tracing out the environment.
Speaker 3: You are intentionally discarding the specific granular correlations between the
Speaker 3: quantum system and the bath that sits in oh I see.
Speaker 3: So in doing so, the specific backflow of information the
Speaker 3: memory can mathematically cancel itself out. In the state evolution,
Speaker 3: the state marches forward looking completely Markovian and divisible.
Speaker 2: It looks clean because we purposely blurred the background to
Speaker 2: focus on the subject exactly.
Speaker 3: But the Heisenberg picture partitions the math entirely differently. The
Speaker 3: state is fixed, so you don't trace out the environment
Speaker 3: in the same way. Instead, the measurement operators have to
Speaker 3: internally encode the environmental backflow to ensure that when you
Speaker 3: finally do the calculation, the end result perfectly matches the
Speaker 3: Schrodinger picture.
Speaker 2: Wow.
Speaker 3: The operators themselves structurally absorb the correlations with the environment, so.
Speaker 2: They basically swallow the history.
Speaker 3: Yes, so when you test the Heisenberg operators for a divisibility,
Speaker 3: that encoded environmental backflow makes it mathematically impossible to slice
Speaker 3: the timeline into independent chunks.
Speaker 2: Because the history is structurally bound to the operator.
Speaker 3: Right, the memory isn't an absolute property of the particle,
Speaker 3: It is a property of the lens. You are using
Speaker 3: to track the particle's relationship with its environment.
Speaker 2: That is wild. It literally keeps a detailed record of
Speaker 2: the past, a hidden diary that is completely invisible if
Speaker 2: you are looking through the wrong lens.
Speaker 3: Yes, it behaves as though the past never happened in
Speaker 3: its state that holds all the secrets and its observables.
Speaker 2: Which fundamentally shatters the idea of a single objective reality
Speaker 2: at the quantum level.
Speaker 3: It really does.
Speaker 2: But let's bring this out of the theoretical math realm
Speaker 2: and into the laboratory, because, as we said at the beginning,
Speaker 2: realizing that a quantum system can harbor hidden memory isn't
Speaker 2: just a fun math puzzle, No, not at all. It
Speaker 2: is an active, potentially catastrophic hazard for anyone trying to
Speaker 2: build machines out of these systems.
Speaker 3: Yeah, it all comes down to the arch nemesis of
Speaker 3: quantum engineering, decoherence.
Speaker 2: Ah, decoherence, the ultimate quantum buzzkill very much so.
Speaker 3: We mentioned earlier that open systems leak information into the environment.
Speaker 3: When equippit, which is the basic building block of a
Speaker 3: quantum computer, leaks that information, it loses its delicate quantum state.
Speaker 2: It decoheres into a boring classical.
Speaker 3: Bit exactly, and quibots are incredibly fragile. To build a
Speaker 3: functioning quantum computer engineers spend literally billions of dollars fighting
Speaker 3: decoherent Right.
Speaker 2: They build those massive dilution refrigerators that look like giant
Speaker 2: gold chandeliers. Right.
Speaker 3: They cool the processors down to a fraction of a
Speaker 3: degree above absolute zero, just trying to quiet the thermal
Speaker 3: noise of the environment.
Speaker 2: But you can never perfectly isolated system. Some noise always
Speaker 2: gets through, no matter how cold it is.
Speaker 3: True, So the second line defense is quantum error correction.
Speaker 3: Engineers write highly complex software algorithms, things like surface codes
Speaker 3: to detect when a quibit has been bumped by the
Speaker 3: environment and fix the error on the fly before the
Speaker 3: whole calculation collapses.
Speaker 2: So what does this all mean for the engineers building
Speaker 2: these things. Let's say I'm a quantum software engineer. I
Speaker 2: run a standard Schrodeners style test on my quibbits state evolution.
Speaker 2: The math says, great news. Your system is more Covian,
Speaker 2: the dynamical map is divisible. Your quibbit has no memory. Okay, naturally,
Speaker 2: I'm going to write my error correction code based on
Speaker 2: the assumption that every single error is just a random,
Speaker 2: isolated event.
Speaker 3: And your error correction code is going to fail catastrophically.
Speaker 2: Wait, really, just completely fail?
Speaker 3: Yes, because the threshold for surface codes to actually work
Speaker 3: relies heavily on the assumption that errors are independent. If
Speaker 3: an error happens to quibit a, it has nothing to
Speaker 3: do with an error happening to quibb a millisecond later.
Speaker 2: But if the system actually has hidden non Marcovia memory
Speaker 2: embedded in its observables.
Speaker 3: Then the environment is orchestrating a correlated wave of errors
Speaker 3: based on past interactions. The errors aren't just random coin
Speaker 3: flips anymore. They are a sequence of events driven by
Speaker 3: that hidden diary.
Speaker 2: Oh man, So if your error correction strategy assumes the
Speaker 2: system is memoryless, you are basically applying random band aids
Speaker 2: to a highly coordinated systemic breakdown.
Speaker 3: Exactly. You fundamentally misdiagnose the mechanics of the failure.
Speaker 2: Wow, you're trying to treat a genetic disease like it's
Speaker 2: a random scrape on the knee. The treatment won't work
Speaker 2: because it doesn't address the underlying historical code.
Speaker 3: That's a great analogy, and what's fascinating here is that
Speaker 3: the Turkey team's research is so vital because it isn't
Speaker 3: just pointing out a new way for quantum computers.
Speaker 2: To fail, right, It's not just bad news.
Speaker 3: It provides the exact mathematical framework to locate and quantify
Speaker 3: where this hidden memory actually lives. And once you can
Speaker 3: map that and diary, you don't just have to blindly
Speaker 3: fight environmental noise anymore. You can exploit it.
Speaker 2: Wait, how do you exploit noise that is actively trying
Speaker 2: to destroy your data.
Speaker 3: By using techniques like dynamic decoupling but supercharged?
Speaker 2: Okay, explain that.
Speaker 3: So if you know exactly how the environment is absorbing
Speaker 3: and returning information over time, because you can finally read
Speaker 3: the hidden memory in the Heisenberg observables, you can actually
Speaker 3: time your control pulses to perfectly intercept that backflow. Always
Speaker 3: you can literally use the environment's memory as a stabilizing
Speaker 3: resource to reinforce the quibot rather than letting it tear
Speaker 3: the system apart. You turn the environment from a chaotic
Speaker 3: enemy into a complex but predictable battery.
Speaker 2: That is a massive paradigm shift. It's the difference between
Speaker 2: like trying to sail a boat by fighting against a
Speaker 2: completely random storm versus realizing you are actually in a
Speaker 2: very complex deep water current. Once you have the mathematical
Speaker 2: tools to map the current, you can angle your sales
Speaker 2: to use the water's momentum to push forward. Researchers must
Speaker 2: be rushing to apply this.
Speaker 3: Oh, absolutely, they are already exploring this in superconducting circuits,
Speaker 3: trapped ions, and photonic systems. And this hidden memory mapping
Speaker 3: extends far beyond just computing.
Speaker 2: Really where else think.
Speaker 3: About quantum metrology. This is the science of using quantum
Speaker 3: entanglement to make ultra precise measurements. We're talking about things
Speaker 3: like detecting the infinitesimal gravitational pull of a passing dark
Speaker 3: matter candidate wow, or mapping microscopic magnetic fields in the
Speaker 3: human brain.
Speaker 2: But those sensors are so sensitive that, like a truck
Speaker 2: driving by a mile away could ruin the data right precisely.
Speaker 3: In metrology, distinguishing between the actual signal you want to
Speaker 3: measure and the noise of the environment is everything. Okay,
Speaker 3: If your sensors observables are harboring hidden memory of past
Speaker 3: environmental interactions and you don't know it, you will interpret
Speaker 3: that memory as a false positive signal, it'll look.
Speaker 2: Like dark matter, but it's just a memory echo exactly.
Speaker 3: So by applying this new dual perspective framework fils yes,
Speaker 3: this can mathematically filter out the hidden diary. This allows
Speaker 3: for a level of sensor precision we previously thought was
Speaker 3: physically impossible.
Speaker 2: That's incredible. It essentially forces every field that relies on
Speaker 2: quantum mechanics, thermodynamics, cryptography, metrology to run their models through
Speaker 2: this new duelens perspective.
Speaker 3: It changes the baseline of how we interact with the
Speaker 3: quantum world.
Speaker 2: So, just to wrap this all up for you listening,
Speaker 2: we started this conversation with a paradox, a machine that
Speaker 2: perfectly remembers and completely forgets at the exact same time.
Speaker 2: And what we've discovered is that memory isn't a fixed
Speaker 2: label you can just slap on a physical object.
Speaker 3: No, it's not. Memory is a property of the relationship
Speaker 3: between the quantum system, the vast chaos of its environment,
Speaker 3: and the specific mathematical lens the observer chooses to apply.
Speaker 2: The shorter year state averages the history away to give
Speaker 2: you a clean probability of the future.
Speaker 3: And the Heisenberg observables internalize the history to ensure the
Speaker 3: physical mechanics of the universe remain balanced.
Speaker 2: The April twenty twenty six discovery by the Turku team
Speaker 2: basically prove that our descriptions of nature are not nature itself.
Speaker 2: The mathematical lens dictates the physical properties we are allowed
Speaker 2: to perceive. The universe allows a particle to keep its
Speaker 2: secrets right out in the open, provided you are looking
Speaker 2: at the state instead of the operator.
Speaker 3: It is an incredibly elegant solution to a profound physical problem,
Speaker 3: But you know, it leaves us with something much deeper
Speaker 3: to consider about how we interact with the world around us.
Speaker 2: Yeah, it really does.
Speaker 3: We spend so much of our time, energy, and resources
Speaker 3: in physics trying to build larger collidors and more sensitive
Speaker 3: detectors just to capture new elusive information. We are totally
Speaker 3: obsessed with uncovering the unknown.
Speaker 2: Right we always want to find the missing puzzle pieces.
Speaker 3: But if nature itself can perfectly hide an entire history
Speaker 3: of complex information right in front of us, a detailed
Speaker 3: diary mathematically woven into the fabric of a system we
Speaker 3: thought was completely wiped clean, just waiting for us to
Speaker 3: shift our perspective from the state to the observable. Other
Speaker 3: fundamental properties of our daily reality are syctically hiding in
Speaker 3: plain sight. Could our understanding of the flow of time itself,
Speaker 3: or even the nature of gravity simply be an artifact
Speaker 3: of the specific mathematical lens we've been stubbornly looking through
Speaker 3: for the last century.